We can extend the meaning of an existing operator by overloading it.
For example, C# overloads the + to do the string concatenation.
The following operators are overloadable:
To implement operators, define static methods to overload the operator.
The following fragment shows a method that implements the addition operator (+) for adding two instances of the type Text:
public static Text operator +(Text t1, Text t2)
The following declares a method that overrides the operator for adding Text and an int:
public static Text operator +(Text w, int i)
We can use the operator like this:
Text newText = text1 + 1;
Note that the order of the arguments is important.
The fragment defines the behavior for a Text + int operation, but not int + Text.
We would need to define another method to support both orderings.
The following code overloads the + operator:
using System;
using System.IO;
public struct MyValue
{
int value;
public MyValue(int semitonesFromA) { value = semitonesFromA; }
public static MyValue operator +(MyValue x, int semitones)
{
return new MyValue(x.value + semitones);
}
}
class Test
{
static void Main()
{
MyValue B = new MyValue(2);
MyValue C = B + 2;
}
}
The following example defines the type Text, which has two overridden addition operators:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Dynamic;
public class Text
{
public string MyString
{
get;
set;
}
public static string operator +(Text w1, Text w2)
{
return w1.MyString + " " + w2.MyString;
}
public static Text operator +(Text w, int i)
{
return new Text() { MyString = w.MyString + i.ToString() };
}
public override string ToString()
{
return MyString;
}
}
public class MainClass
{
static void Main(string[] args)
{
Text word1 = new Text() { MyString = "Hello" };
Text word2 = new Text() { MyString = "World" };
Console.WriteLine("Word1: {0}", word1);
Console.WriteLine("Word2: {0}", word2);
Console.WriteLine("Added together: {0}", word1 + word2);
Console.WriteLine("Added with int: {0}", word1 + 7);
}
}
The output:
Word1: Hello
Word2: World
Added together: Hello World
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