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So i have a situation where i need different amounts of arguments for a function depending on the end result i desire.
I am new to C# and have heard about overloading the function which is not something i have seen before (i started in JavaScript).
But it looks bit dirty, like not a good practice to do even though it does work. Is it generally not a good idea to use overloaded functions, i could probably do an alternative with more work but overloads do make life easier.
It just feels very uncomfortable having more than one method with the same name. Are these considered standard features and acceptable code practice ? Or could it lead to some messy problems in the future that my inexperience does not know about yet and thus i should avoid it ?
Function overloads.
Named actually method overloading. C# does not have a direct distinction to methods which return a value and those that don't. Hence method.
But it looks bit dirty
It is a key component to the language which is a common practice and definitely not frowned upon.
like not a good practice to do even though it does work.
The idea is to provide different variants for a consumer. One consumer may only have X type to use while only Y type is offered. By offering more, the library, and/or instance is more flexible. Plus it lessons failure points by having the consumer convert data to get it into the method.
(i started in JavaScript).
Don't try to program in the style of language which one is accustomed to. Use the specific features of any new language as designed. By trying to do Java in C# or Ruby in C# is foolish. All languages have their design points...program to the language, not to a style of programming.
just feels very uncomfortable having more than one method with the same name.
Coming from a language which is not type safe, that is an understandable reaction. But keep in mind that the compiler is enforcing safety so that widget X is only matched with widget X; it is a true feature and not a gimmick.
Frankly when I see code which does not provide multiple overloads, I view it as either laziness of the developer or some god awful time crunch, hence rushed code.
Don't go overboard...simply provide enough overloads to make the class useable by a majority of consumers.
Or could it lead to some messy problems in the future
If one is not consistent, possibly yes.
So be consistent in the placement of the variables. If an int starts the method, the other method should also start with that same int; if offered. Don't mix the order.
Consider the following class:
public class MyClass
{
public void MyMethod(int a, object b)
{
}
}
If someone else calls your class like this:
new MyClass().MyMethod(1, 1);
And then in a future version of your assembly you add an innocent overload:
public class MyClass
{
public void MyMethod(int a, object b)
{
}
public void MyMethod(object a, int b)
{
}
}
That someone else's code will not compile against the new assembly.
You are correct that method overloading can introduce problems... however it is not always problematic.
Suppose the simple case - you have a method that operates on one Type - T. If you are tempted to add a method overload to handle a second Type U, consider what interfaces and base classes T and U might have in common (including T or U extending one another). If there is a common Type consider making that the argument type at design time (if that's specific enough). If not, then you may need a method overload. A good contrived example might be a method that returns the square of a number. There is no common abstraction for Type's that have an * operator (which you can write your own in C#). So you'd have to make (2) methods to handle an int and a double:
public int SquareMe(int x) { return x * x; }
public double SquareMe(double x) { return x * x; }
If, however, you found yourself wanting to make a method operating on List<T>, IEnumerable<T>, and T[], you may be better off writing the method to accept an IEnumerable<T> (and just calling ToArray() on it immediately to prevent the IEnumerable from expanding multiple times if your code needs it multiple times - if you're just foreach'ing it once, there's no need to expand it) this way you're left with only (1) method to write tests for. Every method, particularly on publicly consumed API's is more to maintain, document, test, automate, etc. Simpler is usually better (but complexity has its place, too). It's difficult to give an algorithm for design of API's (if there was an existing algorithm for such a thing, we could just have the design generated as the output from some hypothetical program, yes?)
When it comes to designing classes and interfaces for public consumption you should be very careful about method overloading (and your entire API, in general - method overloading introducing subtle breaking changes is just one thing to think about - almost any change could be a breaking change). If your API used by everyone, such as Microsoft, all changes to API's have to be very well thought-out and have minimum to 0 breaking changes.
If it's for "internal" use (and you can detect compilation breaks at build time) then if the compiler's happy, method overloading shouldn't be too big of a deal in and of itself. That being said - someone might call a different overload by accident because of what C# will choose. It's probably more important to have explicit method names (Microsoft recommends spelling things out in C#, generally) that intuitively (i.e. subjectively) match the content of what the method does than the concern of overloading.
Like other things, this language features is a trade off between being explicit and implicit and whether or not it's a good idea varies on the situation; method overloading can be both used and abused. In general try to learn the existing practices, patterns and culture of a new language before developing your own style on things so that you can take advantage of everyone's successes and failures before you. Method overloading definitely has its place in C#.
So, you have a situation that would be made easier by a core feature of the language you are using... and you're concerned about that? I wouldn't worry too much.
It might be idea to make an attempt and once you're happy with it take it over to codereview.stackexchange.com to get some feedback.
If the reason for varying signatures is because 'the end result you desire' varies then that's a case for having different functions.
Overloading is helpful when you have a number of optional parameters. If you have five optional parameters it's less obvious what will happen if you specify some but not others. If you create overloads then you can provide different versions of the function with required parameters. Perhaps behind the scenes they can all call a private method with optional parameters, but that remains hidden from public use.
Why not just use an optional parameter?
void Foo (int op = 42)
{
if (x!=42)
//do something
else
}
int x = 33;
Foo();
Foo(x);
I need to find the minimum between 3 values, and I ended up doing something like this:
Math.Min(Math.Min(val1, val2), val3)
It just seems a little silly to me, because other languages use variadic functions for this. I highly doubt this was an oversight though.
Is there any reason why a simple Min/Max function shoundn't be variadic? Are there performance implications? Is there a variadic version that I didn't notice?
If it is a collection (A subclass of IEnumerable<T>) one could easily use the functions in the System.Linq library
int min = new int[] {2,3,4,8}.Min();
Furthermore, it's easy to implement these methods on your own:
public static class Maths {
public static T Min<T> (params T[] vals) {
return vals.Min();
}
public static T Max<T> (params T[] vals) {
return vals.Max();
}
}
You can call these methods with just simple scalars so Maths.Min(14,25,13,2) would give 2.
These are the generic methods, so there is no need to implement this method for each type of numbers (int,float,...)
I think the basic reason why these methods are not implemented in general is that, every time you call this method, an array (or at least an IList object) should be created. By keeping low-level methods one can avoid the overhead. However, I agree one could add these methods to the Math class to make the life of some programmers easier.
CommuSoft has addressed how to accomplish the equivalent in C#, so I won't retread that part.
To specifically address your question "Why aren't C#'s Math.Min/Max variadic?", two thoughts come to mind.
First, Math.Min (and Math.Max) is not, in fact, a C# language feature, it is a .NET framework library feature. That may seem pedantic, but it is an important distinction. C# does not, in fact, provide any special purpose language feature for determining the minimum or maximum value between two (or more) potential values.
Secondly, as Eric Lippert has pointed out a number of times, language features (and presumably framework features) are not "removed" or actively excluded - all features are unimplemented until someone designs, implements, tests, documents and ships the feature. See here for an example.
Not being a .NET framework developer, I cannot speak to the actual decision process that occurred, but it seems like this is a classic case of a feature that simply never rose to the level of inclusion, similar to the sequence foreach "feature" Eric discusses in the provided link.
I think CommuSoft is providing a robust answer that is at least suited for people searching for something along these lines, and that should be accepted.
With that said, the reason is definitely to avoid the overhead necessary for the less likely use case that people want to compare a group rather than two values.
As pointed about by #arx, using a parametric would be unnecessary overhead for the most used case, but it would also be a lot of unnecessary overhead with regards to the loop that would have to be used internally to go through the array n - 1 times.
I can easily see an argument for having created the method in addition to the basic form, but with LINQ that's just no longer necessary.
class my_class
{
public int add_1(int a, int b) {return a + b;}
public func<int, int, int> add_2 = (a, b) => {return a + b;}
}
add_1 is a function whereas add_2 is a delegate. However in this context delegates can forfill a similar role.
Due to precedent and the design of the language the default choice for C# methods should be functions.
However both approaches have pros and cons so I've produced a list. Are there any more advanteges or disadvantages to either approach?
Advantages to conventional methods.
more conventional
outside users of the function see named parameters - for the add_2 syntax arg_n and a type is generally not enough information.
works better with intellisense - ty Minitech
works with reflection - ty Minitech
works with inheritance - ty Eric Lippert
has a "this" - ty CodeInChaos
lower overheads, speed and memory - ty Minitech and CodeInChaos
don't need to think about public\private in respect to both changing and using the function. - ty CodeInChaos
less dynamic, less is permitted that is not known at compile time - ty CodeInChaos
Advantages to "field of delegate type" methods.
more consistant, not member functions and data members, it's just all just data members.
can outwardly look and behave like a variable.
storing it in a container works well.
multiple classes could use the same function as if it were each ones member function, this would be very generic, concise and have good code reuse.
straightforward to use anywhere, for example as a local function.
presumably works well when passed around with garbage collection.
more dynamic, less must be known at compile time, for example there could be functions that configure the behaviour of objects at run time.
as if encapsulating it's code, can be combined and reworked, msdn.microsoft.com/en-us/library/ms173175%28v=vs.80%29.aspx
outside users of the function see unnamed parameters - sometimes this is helpfull although it would be nice to be able to name them.
can be more compact, in this simple example for example the return could be removed, if there were one parameter the brackets could also be removed.
roll you'r own behaviours like inheritance - ty Eric Lippert
other considerations such as functional, modular, distributed, (code writing, testing or reasoning about code) etc...
Please don't vote to close, thats happened already and it got reopened. It's a valid question even if either you don't think the delegates approach has much practical use given how it conflicts with established coding style or you don't like the advanteges of delegates.
First off, the "high order bit" for me with regards to this design decision would be that I would never do this sort of thing with a public field/method. At the very least I would use a property, and probably not even that.
For private fields, I use this pattern fairly frequently, usually like this:
class C
{
private Func<int, int> ActualFunction = (int y)=>{ ... };
private Func<int, int> Function = ActualFunction.Memoize();
and now I can very easily test the performance characteristics of different memoization strategies without having to change the text of ActualFunction at all.
Another advantage of the "methods are fields of delegate type" strategy is that you can implement code sharing techniques that are different than the ones we've "baked in" to the language. A protected field of delegate type is essentially a virtual method, but more flexible. Derived classes can replace it with whatever they want, and you have emulated a regular virtual method. But you could build custom inheritence mechanisms; if you really like prototype inheritance, for example, you could have a convention that if the field is null, then a method on some prototypical instance is called instead, and so on.
A major disadvantage of the methods-are-fields-of-delegate-type approach is that of course, overloading no longer works. Fields must be unique in name; methods merely must be unique in signature. Also, you don't get generic fields the way that we get generic methods, so method type inference stops working.
The second one, in my opinion, offers absolutely no advantage over the first one. It's much less readable, is probably less efficient (given that Invoke has to be implied) and isn't more concise at all. What's more, if you ever use reflection it won't show up as being a method so if you do that to replace your methods in every class, you might break something that seems like it should work. In Visual Studio, the IntelliSense won't include a description of the method since you can't put XML comments on delegates (at least, not in the same way you would put them on normal methods) and you don't know what they point to anyway, unless it's readonly (but what if the constructor changed it?) and it will show up as a field, not a method, which is confusing.
The only time you should really use lambdas is in methods where closures are required, or when it's offers a significant convenience advantage. Otherwise, you're just decreasing readability (basically the readability of my first paragraph versus the current one) and breaking compatibility with previous versions of C#.
Why you should avoid delegates as methods by default, and what are alternatives:
Learning curve
Using delegates this way will surprise a lot of people. Not everyone can wrap their head around delegates, or why you'd want to swap out functions. There seems to be a learning curve. Once you get past it, delegates seem simple.
Perf and reliability
There's a performance loss to invoking delegates in this manner. This is another reason I would default to traditional method declaration unless it enabled something special in my pattern.
There's also an execution safety issue. Public fields are nullable. If you're passed an instance of a class with a public field you'll have to check that it isn't null before using it. This hurts perf and is kind of lame.
You can work around this by changing all public fields to properties (which is a rule in all .Net coding standards anyhow). Then in the setter throw an ArgumentNullException if someone tries to assign null.
Program design
Even if you can deal with all of this, allowing methods to be mutable at all goes against a lot of the design for static OO and functional programming languages.
In static OO types are always static, and dynamic behavior is enabled through polymorphism. You can know the exact behavior of a type based on its run time type. This is very helpful in debugging an existing program. Allowing your types to be modified at run time harms this.
In both static OO and function programming paradigms, limiting and isolating side-effects is quite helpful, and using fully immutable structures is one of the primary ways to do this. The only point of exposing methods as delegates is to create mutable structures, which has the exact opposite effect.
Alternatives
If you really wanted to go so far as to always use delegates to replace methods, you should be using a language like IronPython or something else built on top of the DLR. Those languages will be tooled and tuned for the paradigm you're trying to implement. Users and maintainers of your code won't be surprised.
That being said, there are uses that justify using delegates as a substitute for methods. You shouldn't consider this option unless you have a compelling reason to do so that overrides these performance, confusion, reliability, and design issues. You should only do so if you're getting something in return.
Uses
For private members, Eric Lippert's answer describes a good use: (Memoization).
You can use it to implement a Strategy Pattern in a function-based manner rather than requiring a class hierarchy. Again, I'd use private members for this...
...Example code:
public class Context
{
private Func<int, int, int> executeStrategy;
public Context(Func<int, int, int> executeStrategy) {
this.executeStrategy = executeStrategy;
}
public int ExecuteStrategy(int a, int b) {
return executeStrategy(a, b);
}
}
I have found a particular case where I think public delegate properties are warrented: To implement a Template Method Pattern with instances instead of derived classes...
...This is particularly useful in automated integration tests where you have a lot of setup/tear down. In such cases it often makes sense to keep state in a class designed to encapsulate the pattern rather than rely on the unit test fixture. This way you can easily support sharing the skeleton of the test suite between fixtures, without relying on (sometimes shoddy) test fixture inheritance. It also might be more amenable to parallelization, depending on the implementation of your tests.
var test = new MyFancyUITest
{
// I usually name these things in a more test specific manner...
Setup = () => { /* ... */ },
TearDown = () => { /* ... */ },
};
test.Execute();
Intellisense Support
outside users of the function see unnamed parameters - sometimes this is helpfull although it would be nice to be able to name them.
Use a named delegate - I believe this will get you at least some Intellisense for the parameters (probably just the names, less likely XML docs - please correct me if I'm wrong):
public class MyClass
{
public delegate int DoSomethingImpl(int foo, int bizBar);
public DoSomethingImpl DoSomething = (x, y) => { return x + y; }
}
I'd avoid delegate properties/fields as method replacements for public methods. For private methods it's a tool, but not one I use very often.
instance delegate fields have a per instance memory cost. Probably a premature optimization for most classes, but still something to keep in mind.
Your code uses a public mutable field, which can be changed at any time. That hurts encapsulation.
If you use the field initializer syntax, you can't access this. So field initializer syntax is mainly useful for static methods.
Makes static analysis much harder, since the implementation of that method isn't known at compile-time.
There are some cases where delegate properties/fields might be useful:
Handlers of some sort. Especially if multi-casting (and thus the event subscription pattern) doesn't make much sense
Assigning something that can't be easily described by a simple method body. Such as a memoized function.
The delegate is runtime generated or at least its value is only decided at runtime
Using a closure over local variables is an alternative to using a method and private fields. I strongly dislike classes with lots of fields, especially if some of these fields are only used by two methods or less. In these situations, using a delegate in a field can be preferable to conventional methods
class MyClassConventional {
int? someValue; // When Mark() is called, remember the value so that we can do something with it in Process(). Not used in any other method.
int X;
void Mark() {
someValue = X;
}
void Process() {
// Do something with someValue.Value
}
}
class MyClassClosure {
int X;
Action Process = null;
void Mark() {
int someValue = X;
Process = () => { // Do something with someValue };
}
}
This question presents a false dichotomy - between functions, and a delegate with an equivalent signature. The main difference is that one of the two you should only use if there are no other choices. Use this in your day to day work, and it will be thrown out of any code review.
The benefits that have been mentioned are far outweighed by the fact that there is almost never a reason to write code that is so obscure; especially when this code makes it look like you don't know how to program C#.
I urge anyone reading this to ignore any of the benefits which have been stated, since they are all overwhelmed by the fact that this is the kind of code that demonstrates that you do not know how to program in C#.
The only exception to that rule is if you have a need for one of the benefits, and that need can't be satisfied in any other way. In that case, you'll need to write more comment than code to explain why you have a good reason to do it. Be prepared to answer as clearly as Eric Lippert did. You'd better be able to explain as well as Eric does that you can't accomplish your requirements and write understandable code at the same time.
I thought I'd offer this softball to whomever would like to hit it out of the park. What are generics, what are the advantages of generics, why, where, how should I use them? Please keep it fairly basic. Thanks.
Allows you to write code/use library methods which are type-safe, i.e. a List<string> is guaranteed to be a list of strings.
As a result of generics being used the compiler can perform compile-time checks on code for type safety, i.e. are you trying to put an int into that list of strings? Using an ArrayList would cause that to be a less transparent runtime error.
Faster than using objects as it either avoids boxing/unboxing (where .net has to convert value types to reference types or vice-versa) or casting from objects to the required reference type.
Allows you to write code which is applicable to many types with the same underlying behaviour, i.e. a Dictionary<string, int> uses the same underlying code as a Dictionary<DateTime, double>; using generics, the framework team only had to write one piece of code to achieve both results with the aforementioned advantages too.
I really hate to repeat myself. I hate typing the same thing more often than I have to. I don't like restating things multiple times with slight differences.
Instead of creating:
class MyObjectList {
MyObject get(int index) {...}
}
class MyOtherObjectList {
MyOtherObject get(int index) {...}
}
class AnotherObjectList {
AnotherObject get(int index) {...}
}
I can build one reusable class... (in the case where you don't want to use the raw collection for some reason)
class MyList<T> {
T get(int index) { ... }
}
I'm now 3x more efficient and I only have to maintain one copy. Why WOULDN'T you want to maintain less code?
This is also true for non-collection classes such as a Callable<T> or a Reference<T> that has to interact with other classes. Do you really want to extend Callable<T> and Future<T> and every other associated class to create type-safe versions?
I don't.
Not needing to typecast is one of the biggest advantages of Java generics, as it will perform type checking at compile-time. This will reduce the possibility of ClassCastExceptions which can be thrown at runtime, and can lead to more robust code.
But I suspect that you're fully aware of that.
Every time I look at Generics it gives
me a headache. I find the best part of
Java to be it's simplicity and minimal
syntax and generics are not simple and
add a significant amount of new
syntax.
At first, I didn't see the benefit of generics either. I started learning Java from the 1.4 syntax (even though Java 5 was out at the time) and when I encountered generics, I felt that it was more code to write, and I really didn't understand the benefits.
Modern IDEs make writing code with generics easier.
Most modern, decent IDEs are smart enough to assist with writing code with generics, especially with code completion.
Here's an example of making an Map<String, Integer> with a HashMap. The code I would have to type in is:
Map<String, Integer> m = new HashMap<String, Integer>();
And indeed, that's a lot to type just to make a new HashMap. However, in reality, I only had to type this much before Eclipse knew what I needed:
Map<String, Integer> m = new Ha Ctrl+Space
True, I did need to select HashMap from a list of candidates, but basically the IDE knew what to add, including the generic types. With the right tools, using generics isn't too bad.
In addition, since the types are known, when retrieving elements from the generic collection, the IDE will act as if that object is already an object of its declared type -- there is no need to casting for the IDE to know what the object's type is.
A key advantage of generics comes from the way it plays well with new Java 5 features. Here's an example of tossing integers in to a Set and calculating its total:
Set<Integer> set = new HashSet<Integer>();
set.add(10);
set.add(42);
int total = 0;
for (int i : set) {
total += i;
}
In that piece of code, there are three new Java 5 features present:
Generics
Autoboxing and unboxing
For-each loop
First, generics and autoboxing of primitives allow the following lines:
set.add(10);
set.add(42);
The integer 10 is autoboxed into an Integer with the value of 10. (And same for 42). Then that Integer is tossed into the Set which is known to hold Integers. Trying to throw in a String would cause a compile error.
Next, for for-each loop takes all three of those:
for (int i : set) {
total += i;
}
First, the Set containing Integers are used in a for-each loop. Each element is declared to be an int and that is allowed as the Integer is unboxed back to the primitive int. And the fact that this unboxing occurs is known because generics was used to specify that there were Integers held in the Set.
Generics can be the glue that brings together the new features introduced in Java 5, and it just makes coding simpler and safer. And most of the time IDEs are smart enough to help you with good suggestions, so generally, it won't a whole lot more typing.
And frankly, as can be seen from the Set example, I feel that utilizing Java 5 features can make the code more concise and robust.
Edit - An example without generics
The following is an illustration of the above Set example without the use of generics. It is possible, but isn't exactly pleasant:
Set set = new HashSet();
set.add(10);
set.add(42);
int total = 0;
for (Object o : set) {
total += (Integer)o;
}
(Note: The above code will generate unchecked conversion warning at compile-time.)
When using non-generics collections, the types that are entered into the collection is objects of type Object. Therefore, in this example, a Object is what is being added into the set.
set.add(10);
set.add(42);
In the above lines, autoboxing is in play -- the primitive int value 10 and 42 are being autoboxed into Integer objects, which are being added to the Set. However, keep in mind, the Integer objects are being handled as Objects, as there are no type information to help the compiler know what type the Set should expect.
for (Object o : set) {
This is the part that is crucial. The reason the for-each loop works is because the Set implements the Iterable interface, which returns an Iterator with type information, if present. (Iterator<T>, that is.)
However, since there is no type information, the Set will return an Iterator which will return the values in the Set as Objects, and that is why the element being retrieved in the for-each loop must be of type Object.
Now that the Object is retrieved from the Set, it needs to be cast to an Integer manually to perform the addition:
total += (Integer)o;
Here, a typecast is performed from an Object to an Integer. In this case, we know this will always work, but manual typecasting always makes me feel it is fragile code that could be damaged if a minor change is made else where. (I feel that every typecast is a ClassCastException waiting to happen, but I digress...)
The Integer is now unboxed into an int and allowed to perform the addition into the int variable total.
I hope I could illustrate that the new features of Java 5 is possible to use with non-generic code, but it just isn't as clean and straight-forward as writing code with generics. And, in my opinion, to take full advantage of the new features in Java 5, one should be looking into generics, if at the very least, allows for compile-time checks to prevent invalid typecasts to throw exceptions at runtime.
If you were to search the Java bug database just before 1.5 was released, you'd find seven times more bugs with NullPointerException than ClassCastException. So it doesn't seem that it is a great feature to find bugs, or at least bugs that persist after a little smoke testing.
For me the huge advantage of generics is that they document in code important type information. If I didn't want that type information documented in code, then I'd use a dynamically typed language, or at least a language with more implicit type inference.
Keeping an object's collections to itself isn't a bad style (but then the common style is to effectively ignore encapsulation). It rather depends upon what you are doing. Passing collections to "algorithms" is slightly easier to check (at or before compile-time) with generics.
Generics in Java facilitate parametric polymorphism. By means of type parameters, you can pass arguments to types. Just as a method like String foo(String s) models some behaviour, not just for a particular string, but for any string s, so a type like List<T> models some behaviour, not just for a specific type, but for any type. List<T> says that for any type T, there's a type of List whose elements are Ts. So List is a actually a type constructor. It takes a type as an argument and constructs another type as a result.
Here are a couple of examples of generic types I use every day. First, a very useful generic interface:
public interface F<A, B> {
public B f(A a);
}
This interface says that for some two types, A and B, there's a function (called f) that takes an A and returns a B. When you implement this interface, A and B can be any types you want, as long as you provide a function f that takes the former and returns the latter. Here's an example implementation of the interface:
F<Integer, String> intToString = new F<Integer, String>() {
public String f(int i) {
return String.valueOf(i);
}
}
Before generics, polymorphism was achieved by subclassing using the extends keyword. With generics, we can actually do away with subclassing and use parametric polymorphism instead. For example, consider a parameterised (generic) class used to calculate hash codes for any type. Instead of overriding Object.hashCode(), we would use a generic class like this:
public final class Hash<A> {
private final F<A, Integer> hashFunction;
public Hash(final F<A, Integer> f) {
this.hashFunction = f;
}
public int hash(A a) {
return hashFunction.f(a);
}
}
This is much more flexible than using inheritance, because we can stay with the theme of using composition and parametric polymorphism without locking down brittle hierarchies.
Java's generics are not perfect though. You can abstract over types, but you can't abstract over type constructors, for example. That is, you can say "for any type T", but you can't say "for any type T that takes a type parameter A".
I wrote an article about these limits of Java generics, here.
One huge win with generics is that they let you avoid subclassing. Subclassing tends to result in brittle class hierarchies that are awkward to extend, and classes that are difficult to understand individually without looking at the entire hierarchy.
Wereas before generics you might have classes like Widget extended by FooWidget, BarWidget, and BazWidget, with generics you can have a single generic class Widget<A> that takes a Foo, Bar or Baz in its constructor to give you Widget<Foo>, Widget<Bar>, and Widget<Baz>.
Generics avoid the performance hit of boxing and unboxing. Basically, look at ArrayList vs List<T>. Both do the same core things, but List<T> will be a lot faster because you don't have to box to/from object.
The best benefit to Generics is code reuse. Lets say that you have a lot of business objects, and you are going to write VERY similar code for each entity to perform the same actions. (I.E Linq to SQL operations).
With generics, you can create a class that will be able to operate given any of the types that inherit from a given base class or implement a given interface like so:
public interface IEntity
{
}
public class Employee : IEntity
{
public string FirstName { get; set; }
public string LastName { get; set; }
public int EmployeeID { get; set; }
}
public class Company : IEntity
{
public string Name { get; set; }
public string TaxID { get; set }
}
public class DataService<ENTITY, DATACONTEXT>
where ENTITY : class, IEntity, new()
where DATACONTEXT : DataContext, new()
{
public void Create(List<ENTITY> entities)
{
using (DATACONTEXT db = new DATACONTEXT())
{
Table<ENTITY> table = db.GetTable<ENTITY>();
foreach (ENTITY entity in entities)
table.InsertOnSubmit (entity);
db.SubmitChanges();
}
}
}
public class MyTest
{
public void DoSomething()
{
var dataService = new DataService<Employee, MyDataContext>();
dataService.Create(new Employee { FirstName = "Bob", LastName = "Smith", EmployeeID = 5 });
var otherDataService = new DataService<Company, MyDataContext>();
otherDataService.Create(new Company { Name = "ACME", TaxID = "123-111-2233" });
}
}
Notice the reuse of the same service given the different Types in the DoSomething method above. Truly elegant!
There's many other great reasons to use generics for your work, this is my favorite.
I just like them because they give you a quick way to define a custom type (as I use them anyway).
So for example instead of defining a structure consisting of a string and an integer, and then having to implement a whole set of objects and methods on how to access an array of those structures and so forth, you can just make a Dictionary
Dictionary<int, string> dictionary = new Dictionary<int, string>();
And the compiler/IDE does the rest of the heavy lifting. A Dictionary in particular lets you use the first type as a key (no repeated values).
Typed collections - even if you don't want to use them you're likely to have to deal with them from other libraries , other sources.
Generic typing in class creation:
public class Foo < T> {
public T get()...
Avoidance of casting - I've always disliked things like
new Comparator {
public int compareTo(Object o){
if (o instanceof classIcareAbout)...
Where you're essentially checking for a condition that should only exist because the interface is expressed in terms of objects.
My initial reaction to generics was similar to yours - "too messy, too complicated". My experience is that after using them for a bit you get used to them, and code without them feels less clearly specified, and just less comfortable. Aside from that, the rest of the java world uses them so you're going to have to get with the program eventually, right?
To give a good example. Imagine you have a class called Foo
public class Foo
{
public string Bar() { return "Bar"; }
}
Example 1
Now you want to have a collection of Foo objects. You have two options, LIst or ArrayList, both of which work in a similar manner.
Arraylist al = new ArrayList();
List<Foo> fl = new List<Foo>();
//code to add Foos
al.Add(new Foo());
f1.Add(new Foo());
In the above code, if I try to add a class of FireTruck instead of Foo, the ArrayList will add it, but the Generic List of Foo will cause an exception to be thrown.
Example two.
Now you have your two array lists and you want to call the Bar() function on each. Since hte ArrayList is filled with Objects, you have to cast them before you can call bar. But since the Generic List of Foo can only contain Foos, you can call Bar() directly on those.
foreach(object o in al)
{
Foo f = (Foo)o;
f.Bar();
}
foreach(Foo f in fl)
{
f.Bar();
}
Haven't you ever written a method (or a class) where the key concept of the method/class wasn't tightly bound to a specific data type of the parameters/instance variables (think linked list, max/min functions, binary search, etc.).
Haven't you ever wish you could reuse the algorthm/code without resorting to cut-n-paste reuse or compromising strong-typing (e.g. I want a List of Strings, not a List of things I hope are strings!)?
That's why you should want to use generics (or something better).
The primary advantage, as Mitchel points out, is strong-typing without needing to define multiple classes.
This way you can do stuff like:
List<SomeCustomClass> blah = new List<SomeCustomClass>();
blah[0].SomeCustomFunction();
Without generics, you would have to cast blah[0] to the correct type to access its functions.
Don't forget that generics aren't just used by classes, they can also be used by methods. For example, take the following snippet:
private <T extends Throwable> T logAndReturn(T t) {
logThrowable(t); // some logging method that takes a Throwable
return t;
}
It is simple, but can be used very elegantly. The nice thing is that the method returns whatever it was that it was given. This helps out when you are handling exceptions that need to be re-thrown back to the caller:
...
} catch (MyException e) {
throw logAndReturn(e);
}
The point is that you don't lose the type by passing it through a method. You can throw the correct type of exception instead of just a Throwable, which would be all you could do without generics.
This is just a simple example of one use for generic methods. There are quite a few other neat things you can do with generic methods. The coolest, in my opinion, is type inferring with generics. Take the following example (taken from Josh Bloch's Effective Java 2nd Edition):
...
Map<String, Integer> myMap = createHashMap();
...
public <K, V> Map<K, V> createHashMap() {
return new HashMap<K, V>();
}
This doesn't do a lot, but it does cut down on some clutter when the generic types are long (or nested; i.e. Map<String, List<String>>).
Generics allow you to create objects that are strongly typed, yet you don't have to define the specific type. I think the best useful example is the List and similar classes.
Using the generic list you can have a List List List whatever you want and you can always reference the strong typing, you don't have to convert or anything like you would with a Array or standard List.
the jvm casts anyway... it implicitly creates code which treats the generic type as "Object" and creates casts to the desired instantiation. Java generics are just syntactic sugar.
I know this is a C# question, but generics are used in other languages too, and their use/goals are quite similar.
Java collections use generics since Java 1.5. So, a good place to use them is when you are creating your own collection-like object.
An example I see almost everywhere is a Pair class, which holds two objects, but needs to deal with those objects in a generic way.
class Pair<F, S> {
public final F first;
public final S second;
public Pair(F f, S s)
{
first = f;
second = s;
}
}
Whenever you use this Pair class you can specify which kind of objects you want it to deal with and any type cast problems will show up at compile time, rather than runtime.
Generics can also have their bounds defined with the keywords 'super' and 'extends'. For example, if you want to deal with a generic type but you want to make sure it extends a class called Foo (which has a setTitle method):
public class FooManager <F extends Foo>{
public void setTitle(F foo, String title) {
foo.setTitle(title);
}
}
While not very interesting on its own, it's useful to know that whenever you deal with a FooManager, you know that it will handle MyClass types, and that MyClass extends Foo.
From the Sun Java documentation, in response to "why should i use generics?":
"Generics provides a way for you to communicate the type of a collection to the compiler, so that it can be checked. Once the compiler knows the element type of the collection, the compiler can check that you have used the collection consistently and can insert the correct casts on values being taken out of the collection... The code using generics is clearer and safer.... the compiler can verify at compile time that the type constraints are not violated at run time [emphasis mine]. Because the program compiles without warnings, we can state with certainty that it will not throw a ClassCastException at run time. The net effect of using generics, especially in large programs, is improved readability and robustness. [emphasis mine]"
Generics let you use strong typing for objects and data structures that should be able to hold any object. It also eliminates tedious and expensive typecasts when retrieving objects from generic structures (boxing/unboxing).
One example that uses both is a linked list. What good would a linked list class be if it could only use object Foo? To implement a linked list that can handle any kind of object, the linked list and the nodes in a hypothetical node inner class must be generic if you want the list to contain only one type of object.
If your collection contains value types, they don't need to box/unbox to objects when inserted into the collection so your performance increases dramatically. Cool add-ons like resharper can generate more code for you, like foreach loops.
Another advantage of using Generics (especially with Collections/Lists) is you get Compile Time Type Checking. This is really useful when using a Generic List instead of a List of Objects.
Single most reason is they provide Type safety
List<Customer> custCollection = new List<Customer>;
as opposed to,
object[] custCollection = new object[] { cust1, cust2 };
as a simple example.
In summary, generics allow you to specify more precisily what you intend to do (stronger typing).
This has several benefits for you:
Because the compiler knows more about what you want to do, it allows you to omit a lot of type-casting because it already knows that the type will be compatible.
This also gets you earlier feedback about the correctnes of your program. Things that previously would have failed at runtime (e.g. because an object couldn't be casted in the desired type), now fail at compile-time and you can fix the mistake before your testing-department files a cryptical bug report.
The compiler can do more optimizations, like avoiding boxing, etc.
A couple of things to add/expand on (speaking from the .NET point of view):
Generic types allow you to create role-based classes and interfaces. This has been said already in more basic terms, but I find you start to design your code with classes which are implemented in a type-agnostic way - which results in highly reusable code.
Generic arguments on methods can do the same thing, but they also help apply the "Tell Don't Ask" principle to casting, i.e. "give me what I want, and if you can't, you tell me why".
I use them for example in a GenericDao implemented with SpringORM and Hibernate which look like this
public abstract class GenericDaoHibernateImpl<T>
extends HibernateDaoSupport {
private Class<T> type;
public GenericDaoHibernateImpl(Class<T> clazz) {
type = clazz;
}
public void update(T object) {
getHibernateTemplate().update(object);
}
#SuppressWarnings("unchecked")
public Integer count() {
return ((Integer) getHibernateTemplate().execute(
new HibernateCallback() {
public Object doInHibernate(Session session) {
// Code in Hibernate for getting the count
}
}));
}
.
.
.
}
By using generics my implementations of this DAOs force the developer to pass them just the entities they are designed for by just subclassing the GenericDao
public class UserDaoHibernateImpl extends GenericDaoHibernateImpl<User> {
public UserDaoHibernateImpl() {
super(User.class); // This is for giving Hibernate a .class
// work with, as generics disappear at runtime
}
// Entity specific methods here
}
My little framework is more robust (have things like filtering, lazy-loading, searching). I just simplified here to give you an example
I, like Steve and you, said at the beginning "Too messy and complicated" but now I see its advantages
Obvious benefits like "type safety" and "no casting" are already mentioned so maybe I can talk about some other "benefits" which I hope it helps.
First of all, generics is a language-independent concept and , IMO, it might make more sense if you think about regular (runtime) polymorphism at the same time.
For example, the polymorphism as we know from object oriented design has a runtime notion in where the caller object is figured out at runtime as program execution goes and the relevant method gets called accordingly depending on the runtime type. In generics, the idea is somewhat similar but everything happens at compile time. What does that mean and how you make use of it?
(Let's stick with generic methods to keep it compact) It means that you can still have the same method on separate classes (like you did previously in polymorphic classes) but this time they're auto-generated by the compiler depend on the types set at compile time. You parametrise your methods on the type you give at compile time. So, instead of writing the methods from scratch for every single type you have as you do in runtime polymorphism (method overriding), you let compilers do the work during compilation. This has an obvious advantage since you don't need to infer all possible types that might be used in your system which makes it far more scalable without a code change.
Classes work the pretty much same way. You parametrise the type and the code is generated by the compiler.
Once you get the idea of "compile time", you can make use "bounded" types and restrict what can be passed as a parametrised type through classes/methods. So, you can control what to be passed through which is a powerful thing especially you've a framework being consumed by other people.
public interface Foo<T extends MyObject> extends Hoo<T>{
...
}
No one can set sth other than MyObject now.
Also, you can "enforce" type constraints on your method arguments which means you can make sure both your method arguments would depend on the same type.
public <T extends MyObject> foo(T t1, T t2){
...
}
Hope all of this makes sense.
I once gave a talk on this topic. You can find my slides, code, and audio recording at http://www.adventuresinsoftware.com/generics/.
Using generics for collections is just simple and clean. Even if you punt on it everywhere else, the gain from the collections is a win to me.
List<Stuff> stuffList = getStuff();
for(Stuff stuff : stuffList) {
stuff.do();
}
vs
List stuffList = getStuff();
Iterator i = stuffList.iterator();
while(i.hasNext()) {
Stuff stuff = (Stuff)i.next();
stuff.do();
}
or
List stuffList = getStuff();
for(int i = 0; i < stuffList.size(); i++) {
Stuff stuff = (Stuff)stuffList.get(i);
stuff.do();
}
That alone is worth the marginal "cost" of generics, and you don't have to be a generic Guru to use this and get value.
Generics also give you the ability to create more reusable objects/methods while still providing type specific support. You also gain a lot of performance in some cases. I don't know the full spec on the Java Generics, but in .NET I can specify constraints on the Type parameter, like Implements a Interface, Constructor , and Derivation.
Enabling programmers to implement generic algorithms - By using generics, programmers can implement generic algorithms that work on collections of different types, can be customized, and are type-safe and easier to read.
Stronger type checks at compile time - A Java compiler applies strong type checking to generic code and issues errors if the code violates type safety. Fixing compile-time errors is easier than fixing runtime errors, which can be difficult to find.
Elimination of casts.
I'm looking at the new C# feature of tuples. I'm curious, what problem was the tuple designed to solve?
What have you used tuples for in your apps?
Update
Thanks for the answers thus far, let me see if I have things straight in my mind.
A good example of a tuple has been pointed out as coordinates. Does this look right?
var coords = Tuple.Create(geoLat,geoLong);
Then use the tuple like so:
var myLatlng = new google.maps.LatLng("+ coords.Item1 + ", "+ coords.Item2 + ");
Is that correct?
When writing programs it is extremely common to want to logically group together a set of values which do not have sufficient commonality to justify making a class.
Many programming languages allow you to logically group together a set of otherwise unrelated values without creating a type in only one way:
void M(int foo, string bar, double blah)
Logically this is exactly the same as a method M that takes one argument which is a 3-tuple of int, string, double. But I hope you would not actually make:
class MArguments
{
public int Foo { get; private set; }
... etc
unless MArguments had some other meaning in the business logic.
The concept of "group together a bunch of otherwise unrelated data in some structure that is more lightweight than a class" is useful in many, many places, not just for formal parameter lists of methods. It's useful when a method has two things to return, or when you want to key a dictionary off of two data rather than one, and so on.
Languages like F# which support tuple types natively provide a great deal of flexibility to their users; they are an extremely useful set of data types. The BCL team decided to work with the F# team to standardize on one tuple type for the framework so that every language could benefit from them.
However, there is at this point no language support for tuples in C#. Tuples are just another data type like any other framework class; there's nothing special about them. We are considering adding better support for tuples in hypothetical future versions of C#. If anyone has any thoughts on what sort of features involving tuples you'd like to see, I'd be happy to pass them along to the design team. Realistic scenarios are more convincing than theoretical musings.
Tuples provide an immutable implementation of a collection
Aside from the common uses of tuples:
to group common values together without having to create a class
to return multiple values from a function/method
etc...
Immutable objects are inherently thread safe:
Immutable objects can be useful in multi-threaded applications. Multiple threads can act on data represented by immutable objects without concern of the data being changed by other threads. Immutable objects are therefore considered to be more thread-safe than mutable objects.
From "Immutable Object" on wikipedia
It provides an alternative to ref or out if you have a method that needs to return multiple new objects as part of its response.
It also allows you to use a built-in type as a return type if all you need to do is mash-up two or three existing types, and you don't want to have to add a class/struct just for this combination. (Ever wish a function could return an anonymous type? This is a partial answer to that situation.)
It's often helpful to have a "pair" type, just used in quick situations (like returning two values from a method). Tuples are a central part of functional languages like F#, and C# picked them up along the way.
very useful for returning two values from a function
Personally, I find Tuples to be an iterative part of development when you're in an investigative cycle, or just "playing". Because a Tuple is generic, I tend to think of it when working with generic parameters - especially when wanting to develop a generic piece of code, and I'm starting at the code end, instead of asking myself "how would I like this call to look?".
Quite often I realise that the collection that the Tuple forms become part of a list, and staring at List> doesn't really express the intention of the list, or how it works. I often "live" with it, but find myself wanting to manipulate the list, and change a value - at which point, I don't necessarily want to create a new Tuple for that, thus I need to create my own class or struct to hold it, so I can add manipulation code.
Of course, there's always extension methods - but quite often you don't want to extend that extra code to generic implementations.
There have been times I'm wanted to express data as a Tuple, and not had Tuples available. (VS2008) in which case I've just created my own Tuple class - and I don't make it thread safe (immutable).
So I guess I'm of the opinion that Tuples are lazy programming at the expense of losing a type name that describes it's purpose. The other expense is that you have to declare the signature of the Tuple whereever it's used as a parameter. After a number of methods that begin to look bloated, you may feel as I do, that it is worth making a class, as it cleans up the method signatures.
I tend to start by having the class as a public member of the class you're already working in. But the moment it extends beyond simply a collection of values, it get's it's own file, and I move it out of the containing class.
So in retrospect, I believe I use Tuples when I don't want to go off and write a class, and just want to think about what I've writing right now. Which means the signature of the Tuple may change quite a lot in the text half an hour whilst I figure out what data I am going to need for this method, and how it's returning what ever values it will return.
If I get a chance to refactor code, then often I'll question a Tuple's place in it.
Old question since 2010, and now in 2017 Dotnet changes and become more smart.
C# 7 introduces language support for tuples, which enables semantic names for the fields of a tuple using new, more efficient tuple types.
In vs 2017 and .Net 4.7 (or installing nuget package System.ValueTuple), you can create/use a tuple in a very efficient and simple way:
var person = (Id:"123", Name:"john"); //create tuble with two items
Console.WriteLine($"{person.Id} name:{person.Name}") //access its fields
Returning more than one value from a method:
public (double sum, double average) ComputeSumAndAverage(List<double> list)
{
var sum= list.Sum();
var average = sum/list.Count;
return (sum, average);
}
How to use:
var list=new List<double>{1,2,3};
var result = ComputeSumAndAverage(list);
Console.WriteLine($"Sum={result.sum} Average={result.average}");
For more details read: https://learn.microsoft.com/en-us/dotnet/csharp/tuples
A Tuple is often used to return multiple values from functions when you don’t want to create a specific type. If you're familiar with Python, Python has had this for a long time.
Returning more than one value from a function. getCoordinates() isn't very useful if it just returns x or y or z, but making a full class and object to hold three ints also seems pretty heavyweight.
A common use might be to avoid creating classes/structs that only contains 2 fields, instead you create a Tuple (or a KeyValuePair for now).
Usefull as a return value, avoid passing N out params...
I find the KeyValuePair refreshing in C# to iterate over the key value pairs in a Dictionary.
Its really helpful while returning values from functions. We can have multiple values back and this is quite a saver in some scenarios.
I stumbled upon this performance benchmark between Tuples and Key-Value pairs and probably you will find it interesting. In summary it says that Tuple has advantage because it is a class, therefore it is stored in the heap and not in the stack and when passed around as argument its pointer is the only thing that is going. But KeyValuePair is a structs so it is faster to allocate but it is slower when used.
http://www.dotnetperls.com/tuple-keyvaluepair