In C#, I am using a library that defines an enum. I would like to allow consumers of my code (in a different assembly) to pass in an enum value as a parameter to one of my functions without having to reference the underlying library themselves.
Is there a way for me to expose the library's enumeration to my consumers?
You could define your own enum with the values you want to support, expose that to your consumers, and simply convert it to the library's enum before you call into it. Since enums are just numbers behind the scenes, it's easy to convert one enum's values to another's.
You can offer an overload that takes an int, describe which values are valid, then perform the cast yourself. Alternatively, you can offer a different enumeration in your library, then convert it before calling into the second library.
I realy don't know, which rational reason is doing this ( combination of "consumer call method from type in my assembly" and "consumer doesn't have my assembly as reference" ), but there are 2 ways.
The first ( recommended ):
You should split your assembly into two. One with enum type definition and the second with the functions. Consumers will reference only "first" assembly.
The second ( not recommended ):
You can use a (sbyte/(u)short/(u)int/(u)long in parameters instead of enums.
But I think, you have a mismatch design of object model.
Related
I am viewing tuts+ video titled Design Patterns in C#. In it, the instructor says:
"Interfaces are contracts. They are data types that define properties and methods that we have to implement within a class."
My question: Is this correct, that is, are interfaces really data types in C#?
From the C# programming guide:
C# is a strongly-typed language. Every variable and constant has a
type, as does every expression that evaluates to a value. Every method
signature specifies a type for each input parameter and for the return
value.
(...)
You use the struct, class, interface, and enum constructs to create
your own custom types.
So yes, interfaces are considered first class types in the .NET world. Anyway I find the term "data type" confusing in that context, I think that saying just "type" is more correct.
By the term datatype, the instructor must have hinted that Interfaces declare the type that has to be defined later.
If you consider the usage of an Interface, it does the same. It helps us to declare the methods but gives away the freedom to the developers to define it as per their need.
Hope it clears your doubts.
Interface can be considered as reference data type.
A data type in programming language is a set of data with values having predefined characteristics .
In Object Oriented programming, a programmer can create new data types to suit the application requirements.
With object-oriented programming, a programmer can create new data types to meet application needs. Such an exercise as known as "data abstraction" and the result is a new class of data. Such a class can draw upon the "built-in" data types such as number integers and characters. For example, a class could be created that would abstract the characteristics of a purchase order. The purchase order data type would contain the more basic data types of numbers and characters and could also include other object defined by another class. The purchase order data type would have all of the inherent services that a programming language provided to its built-in data types.
Source
Currently, I'm reading C# 5.0 in a Nutshell and in the Type Basics (located at Chapter 2) subtopic the term symmetry of predefined types and custom types is introduced...
...why the author talks about symmetry between those types? What are the argument to say that types are symmetric?
This is the original paragraph:
A beautiful aspect of C# is that predefined types and custom types have few differences. The predefined int type serves as a blueprint for integers. It holds data -32 bits- and provides function members that use that data, such as ToString. Similarly, our custom UnitConverter type acts as a blueprint for unit conversions. It holds data -the ratio- and provides function members to use that data.
The meaning of the text is that all of the types in the language "behave like objects". For example, you can do this:
int i = 42;
Console.WriteLine(i.ToString()); // called a method on an int
as easily as you can do this:
DateTime d = DateTime.Now;
Console.WriteLine(d.ToString()); // called a method on a DateTime
That is, if you did not know the types of i and d you would not be able to deduce anything by just reading the code that calls .ToString().
Contrast this with a language like C++:
std::string s = "hello";
std::cout << s.length();
int i = 42;
// ...but you cannot invoke any method on i; "ints are special"
Here the fact that s.length() compiles tells us that s is not an int, or a pointer, or any other primitive type.
This uniformity does not buy you anything from a technical standpoint, but it is nevertheless a welcome feature -- especially if you are just learning the language.
I believe the author's point is that built-in types and custom types are both meant to serve similar purposes; hold data and provide mechanisms for using that data. I believe there is also a veiled reference in there that both built-in objects and custom objects inherit from System.Object, thus they share similar abilities (i.e. ToString()).
I do not necessarily agree with term 'symmetry', but that is my two cents on the topic.
There are languages where you can't create type that behave similarly to something that is built in like int. In C# one can create type with all properties of 'int' (which is synonym of System.Int32) - value type with +/-/=operation.
I.e. in JavaScript one can't create another Array type or string type. In Java value types are (were?) not present, so type equivalent to 'int' can't be written by programmer ( Does Java make distinction between value type and reference type ).
I am reading the latest edition of this book for C# 10 and had the same question. I like all of the answers so far provided, but have one additional point: this is a reference to the utility of C#'s unified type system, which the author mentions briefly in Chapter 1 under the section 'Object Orientation':
Unified type system
The fundamental building block in C# is an encapsulated unit of data and functions called a type. C# has a unified type system in which all types ultimately share a common base type. This means that all types, whether they represent business objects or are primitive types such as numbers, share the same basic functionality. For example, an instance of any type can be converted to a string by calling its ToString() method.
To distill the author's writing and the comments from others down into a few points:
The type system of C# is unified, in that all types inherit from the common System.Object type.
Logically, type components can be logically grouped into two components: data members and function members.
Practically, because types behave like objects (they all have some data and/or behavior); developers can expect a minimum set of functionality from all types when using C#, such as the ability to call .ToString(), among other things.
These three points seem to be what the author had in mind when he referred to the C# type system having a 'symmetric beauty'.
One of the benefits with C++ templates is that you (implicitly) can require a certain type signature (e.g. type T needs to have a function x that takes no parameters and returns an int). Does C# generics support something similar?
I am aware of constraints based on base class or interface but this is not what I am looking for.
(As a C++ programmer learning C# I might be mistaken that this is a feature that you would want in C#. Any comments on this would be appriciated as well...)
Nothing except for the constraints you have already seen (which do, to be fair, cover a lot of common scenarios). There are some common workarounds:
dynamic, in 4.0
manual duck-typing using either reflection or IL generation etc
none of these have static type-checking etc, though.
Yes, through an interface. You can define a generic object that has a type that must have a specific interface implemented. Within that interface, you would essentially be forcing any object added to that generic, list for instance, to have a specific signature.
Whether or not that's what you're not looking for, that's how you accomplish it. :)
No, this is not possible. It's mainly caused by the differences between C++ templates and C# generics:
When you compile C++ template, the resulting code has types like vector<int> and vector<string>. This means the compiler has to know all the possible type parameters, but it also means it can check them for correctness.
When you compile C# generic type, you are actually creating just one generic type: List<T>. Because of this, the C# compiler doesn't have to know all the possible types at compile type, which means you can have generic types in binary libraries, which is not possible with C++. But this also means that you can't check all the types. To be able to do something like that, there are constraints, but they can't do several things C++'s compile time checking can, like checking the presence of certain methods (without using interface or some base class) or the presence of suitable operators.
In C# 4, you can achieve effect somewhat similar to this kind of templates using dynamic, but this does no compile-time checking, which means you lose safety – you can put in a type that doesn't have the appropriate members and you won't find out until you reach that line of code at runtime.
No. This is what interfaces are for. Create an interface that defined the contract you want to enforce in the type constraints. Then specify that in the constraints.
Nope, not supported in c#. Like you said, the closest thing requires you to have the classes implement a common interface.
You could try to mimic the behavior with reflection, by looking for the method by the signature, but that's a runtime constraint, and not a compile-time constraint.
There are 5 types of constraints you can put onto generics in .Net:
Derivation constraints state the ascendancy of a type parameter.
Interface constraints are interfaces that are implemented by the type parameter.
Value type constraints restrict a type parameter to a value type.
Reference type constraints restrict a type parameter to a reference type.
Constructor constraints stipulate that the type parameter has a default or parameterless constructor.
This page shows more information.
No, C# does not have constraints like that.
As you know, generic constraints can only enforce inheritance of a base class or an interface, or a few other constraints (constructor constraint new(), reference type constraint class, value type constraint struct).
You might be able to achieve your desired behavior using delegates, and there are many Generic delegates available.
For example, Func<int> is a delegate that takes no parameters and returns an int. Func<string, DateTime, int> takes a string and DateTime and returns an int, etc...
I am writing a RationalNumber class in C# and would like to make it generic, but only allowing integers (int, byte, UInt32, my own BigInt class ...) as inputs - it doesn't make sense to have a rational number based on floats or even regular objects like Control.
However, it doesn't seem that I can filter out non-integer types when declaring the class.
Did I overlook something?
No you can't.
And you have the additional problem that there is no arithmetic constraint either. So there is no statically typed way to use the operators of your type argument either. So you'll need to use dynamic which is slower (unless they improved the runtime/jitter since .net 3.5).
Some projects with similar problems didn't make the class generic at all, and used a code generator to specialize it instead.
I have a method with a default parameter:
void Test(int? iRange = null);
When trying to expose my class to COM, I get a warning:
Type library exporter encountered an generic type instance in a signature. Generic code may not be exported to COM. Is it possible to some how expose this method?
Edit
Sorry, i think this is to do with the nullable parameter (not the default parameter) I copied the original method signature incorrectly.
I came across something like this a couple of years ago, COM does not support generics and so anything you expose to COM must be generics free.
In this case "int? iRange" is just shorthand for "Nullable<int> iRange" and as such causes the error. You may have to find another way to express whatever it is you use null to express. You could add another argument or use an otherwise unused value of iRange (0, -1 and int.MinValue come to mind as possibilities - I would recommend providing the value as a const if you choose this option).