Is there a way I can overload primitives, for example addition with doubles? I want to automatically round the doubles whenever an operation is performed. My current code is this:
class Test{
public static double operator +(double x, double y){
return Math.Round(x + y)
}
}
but there's an unfortunate error that says "One of the parameters of a binary operator must be the containing type".
No, and this would be horrible. Users using your library would suddenly get different behaviors from their double variables!
You can write and use a wrapper object however:
public struct MyDouble
{
public double Value {get; set;}
public MyDouble(double initValue)
{
Value = initValue;
}
public static double operator +(MyDouble x, MyDouble y){
return Math.Round(x.Value + y.Value)
}
}
You can also make it castable to/from a double, among other options. This way users know they are using your object and won't be surprised when their math operations are rounded.
If you want to assign from a simple double, you would need to define an implicit operator, similar to that of Nullable<T> (source):
public static implicit operator MyDouble(double value) {
return new MyDouble(value);
}
You can't overload operators on primitive types. This would cause havoc in your codebase.
What you can do instead, is to create a simple wrapper around the primitive type, let's say RoundedDouble:
public struct RoundedDouble : IEquatable<RoundedDouble>, IComparable<RoundedDouble>
{
public readonly double Value;
public RoundedDouble(double value)
{
Value = Math.Round(value); // Or anything else
}
public static implicit operator RoundedDouble(double value)
{
return new RoundedDouble(value);
}
public static implicit operator double(RoundedDouble wrapper)
{
return wrapper.Value;
}
public int GetHashCode()
{
return Value.GetHashCode();
}
public bool Equals(object other)
{
if (other is RoundedDouble)
return ((RoundedDouble)other).Value == Value;
return false;
}
public string ToString()
{
return Value.ToString();
}
// Add your operators here, and implement the interfaces
}
This is a structure. It has the same value semantics as a double.
Extend it by adding the operators, and by implementing at least IEquatable<RoundedDouble> and IComparable<RoundedDouble>.
Related
I know there is no such thing like Operator Overloading in Java and C#. A task is given to me by my teacher to achieve operator overloading in any of these languages. I don't know the deep concepts of these languages, only basic OOP. So can any one tell is there any other way to achieve this?
There is a thing called operator overloading in C#, check out this code snippet from MSDN:
public struct Complex
{
public int real;
public int imaginary;
public Complex(int real, int imaginary)
{
this.real = real;
this.imaginary = imaginary;
}
// Declare which operator to overload (+), the types
// that can be added (two Complex objects), and the
// return type (Complex):
public static Complex operator +(Complex c1, Complex c2)
{
return new Complex(c1.real + c2.real, c1.imaginary + c2.imaginary);
}
}
Full list of overloadable operators
As des has shown, C# does have operator overloading. Java, on the other hand, does not. The way Java compares that two objects are equal is done through overriding the method equals(Object), which is inherited from the base object java.lang.Object. Here's an example usage:
public class MyClass {
private int value;
#Override
public boolean equals(Object o) {
return o instanceof MyClass && ((MyClass)o).value == this.value;
}
}
Of course this is only a workaround for replicating overloading the == operator. For other operators, such as >= or <= there is nothing. However, you can use OO to sort of recreate it by using a common interface:
interface Overloadable<T> {
public boolean isGreaterThan(T other);
public boolean isLessThan(T other);
}
public class MyClass implements Overloadable<MyClass> {
private int value;
#Override
public boolean equals(Object o) {
return o instanceof MyClass && ((MyClass)o).value == this.value;
}
#Override
public boolean isGreaterThan(MyClass other) {
return this.value > other.value;
}
#Override
public boolean isLessThan(MyClass other) {
return this.value < other.value;
}
}
This is by no means real operator overloading because, well, you're not overloading the operators. It does however provide the ability to compare objects in the same way.
So the compiler will not allow me to overrload the == and != operators of my class. Here is what the class looks like:
public class Item
{
public string _name;
public double _weight;
public decimal _wholesalePrice;
public int _quantity;
public Item(string name, double weight, decimal wholesalePrice, int quantity)
{
_name = name;
_weight = weight;
_wholesalePrice = wholesalePrice;
_quantity = quantity;
}
public static override bool operator ==(Item left, Item right)
{
if (left._name == right._name)
{
return true;
}
return false;
}
public static override bool operator !=(Item left,Item right)
{
return !(left == right);
}
}
The compiler keeps telling me "The modifier 'override' is not valid for this item. At first I thought I might not have declared a base method as virtual, but my class does is not derived. Any ideas what's happening?
You cannot declare an override unless you have derived the class from a parent class. You also cannot declare override on a static method. Have you tried removing override all together? That seems to work for me...
public class Item
{
public string _name;
public double _weight;
public decimal _wholesalePrice;
public int _quantity;
public Item(string name, double weight, decimal wholesalePrice, int quantity)
{
_name = name;
_weight = weight;
_wholesalePrice = wholesalePrice;
_quantity = quantity;
}
public static bool operator ==(Item left, Item right)
{
if (left._name == right._name)
{
return true;
}
return false;
}
public static bool operator !=(Item left, Item right)
{
return !(left == right);
}
}
As a side note, if you override the == and != operators, it's also good practice to override the GetHashCode and Equals methods.
You are deriving your class from the class Object, which does not have an == or != operator. So you cannot override those operators.
In addition, you cannot override a static operator or method, you can only override instance methods.
Finally, note that override and overload are two very different things. An overload is where you have multiple definitions of methods with the same name but different signatures (eg. different parameters).
The short answer is that the syntax is public static bool operator ==(Item left, Item right) without the override keyword.
This is called operator overloading, not overriding.
You may think of == as a kind of static method (inside an imaginary "global" class) taking two parameters. When the compiler sees something like
xxx == yyy
it uses overload resolution to find out which == to use. This is analogous to
Meth(xxx, yyy)
where the compiler considers overloads like Meth(Object, Object), Meth(String, String), Meth(Item, Item) and finds out which of them (if any) fits best to the compile-time types of xxx and yyy.
This is just an anolgy, of course, but helps remembering why you include static and not override when you change the == operator.
My brain has turned to jelly, or I'm having an out of mind experience, or something. I'm tinkering with a class hierarchy that looks a bit like this:
My Money class looks like this:
public abstract class Money
{
public int Amount { get; set; }
public static bool operator ==(Money leftSide, Money rightSide)
{
// Money can only be equal if it is in the same currency.
if (leftSide.GetType() != rightSide.GetType()) return false;
return leftSide.Amount == rightSide.Amount;
}
public static bool operator !=(Money leftSide, Money rightSide)
{
// If the currencies are different, the amounts are always considered unequal.
if (leftSide.GetType() != rightSide.GetType()) return true;
return leftSide.Amount != rightSide.Amount;
}
public static Money operator *(Money multiplicand, int multiplier)
{
var result = multiplicand * multiplier;
return result;
}
public static Dollar Dollar(int amount)
{
return new Dollar(amount);
}
public static Franc Franc(int amount)
{
return new Franc(amount);
}
}
My Dollar operator * looks like this:
public static Dollar operator *(Dollar multiplicand, int multiplier)
{
var result = multiplicand.Amount * multiplier;
return new Dollar(result);
}
Now, if I run this test code, I get a Stack overflow (wahoo!)
{
Money fiveDollars = Money.Dollar(5);
Money timesTwo = fiveDollars*2;
}
I had expected that this would recursively call the subclass (Dollar) operator *, which would return a definite result since (Dollar * int) is defined non-recursively. Since this doesn't work, the alternative is that I have done something dumb. Why doesn't this work? What would be the right way to get this behaviour?
You seem to have left out .Amount
public static Money operator *(Money multiplicand, int multiplier)
{
var result = multiplicand.Amount * multiplier;
return result;
}
The problem is that you expect that you can override operators in derived classes and expect dynamic binding. This is not the way it works in C#. Operators are overloaded and the actual overload is chosen compile-time. This means that the following code is recursive and calls itself:
public static Money operator *(Money multiplicand, int multiplier)
{
var result = multiplicand * multiplier;
return result;
}
Another example where you can see the difference between operator overloading and method overriding is this:
int a = 5;
int b = 5;
Console.WriteLine(a == b); // true
Console.WriteLine(a.Equals(b)); // true
Console.WriteLine((object)a == (object)b); // false
Console.WriteLine(((object)a).Equals((object)b)); // true
In the third case, C# treats a and b as objects instead of integers, so it uses the default == operator that is used for objects: comparing references (in this case the references of boxed integers).
This can make it awkward to define operators on a class hierarchy where you want to redefine the operators in derived classes. It is especially awkward when the behavior depends on the combination of both operands, since C# (and most other OOP languages) lacks support for multiple dispatch. You can solve this by using the visitor pattern, but I think in this case you should reconsider if using subclasses for each currency is the best solution.
public class SampleClass {
public int value;
public SampleClass(int v)
{ value = v; }
}
// i want to access value like this
SampleClass sc = new SampleClass(5);
int i = sc;
Is there a way to do this in C#? I don't want to have to say sc.Value every time i need to access the value.
Use an implicit conversion:
public class SampleClass {
public int value;
public SampleClass(int v)
{ value = v; }
public static implicit operator int (SampleClass c)
{
return c.value;
}
}
You should look into properties however.
You can do it by including an implicit conversion from SampleClass to int:
public static implicit operator int(SampleClass s)
{
return s.value;
}
... but I would strongly recommend that you don't do so, or at least that you think very carefully beforehand. Implicit conversions make it harder to reason about the language in various ways (consider things like overload resolution, for example).
Very, very occasionally it's a good idea to introduce implicit conversions - for example LINQ to XML makes great use of it with string to XNamespace and string to XName conversions - but I wouldn't do it here just to avoid having to use .Value.
It's slightly more reasonable to make an explicit conversion (just change implicit to explicit in the operator conversion) in that at least that makes it clear-ish what's going on in the calling code... but at that point there's really not much difference in source size between a cast to int and using .Value.
(And as suggested elsewhere, don't make fields public - use properties instead.)
Take a look at this. You need to overload the implicit cast operator for int.
Yes, it's possible. You need to implement implicit for your SampleClass:
Here it is:
public class SampleClass
{
public int Value;
public SampleClass(int v)
{
Value = v;
}
public static implicit operator int(SampleClass d)
{
return d.Value;
}
}
let's say I have a list of decimals :
List<decimal> values;
and 2 function to display a decimal :
string DisplayPct(decimal pct)
{
return pct.ToString("0.00 %");
}
string DisplayValue(decimal val)
{
return val.ToString("0.00");
}
What would be the best mechanism to implement so I could know which function to call depending on the value?
I would have liked to have for instance typedefs in C#. That way, I could have declared a type Percent and a type Decimal that would both represent decimal values, but then I could know how to display the value based on its type.
Any equivalent in C# ?
Thanks
Here are my classes :
public class Percent
{
public decimal value;
public Percent(decimal d) { value = d; }
public static implicit operator Percent(decimal d) { return new Percent(d); }
public static implicit operator decimal(Percent p) { return p.value; }
}
public class DecimalPrecise
{
public decimal value;
public DecimalPrecise(decimal d) { value = d; }
public static implicit operator DecimalPrecise(decimal d) { return new DecimalPrecise(d); }
public static implicit operator decimal(DecimalPrecise d) { return d.value; }
}
Wrap percent in a class. A bit of work on your part. Just make sure to define the implicit operator to capture decimals, and some of the other operations and ToString as you require.
It sounds like you want two classes: a decimal and a percent. Each one will have a ToString that prints appropriately. If they both have the same interface, you can have a collection of both in a List using that common interface.