EN CSharp Keyword operator

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C#: operator

Handbook C# · Practical Guide

Specifies the supported operation behavior for the custom type. The number of parameters and the static/instance form depend on the operator.

Simple example (Example.cs)

Save this example separately as Example.cs. Run it independently of the other examples on this page.

Example.cs:

// PROJECT-EXAMPLE
var sum = new Count(2) + new Count(3);
System.Console.WriteLine(sum.Value);
readonly record struct Count(int Value)
{
    public static Count operator +(Count a, Count b) => new(a.Value + b.Value);
}

Result:

5

Syntax

public static Type operator +(Type left, Type right) => ...;

Compound assignment operators as instance members and instance ++/-- are added to C# 14. ==/!= and corresponding comparisons require proper pairwise declarations.

Example 1: simple form

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using System.IO;
using System.Runtime.InteropServices;
using System.Runtime.CompilerServices;

public static class Program
{
    public static async Task Main(string[] args)
    {
        Amount total = new Amount(2) + new Amount(3);
        Console.WriteLine(total.Value);
    }
}
public readonly record struct Amount(int Value) { public static Amount operator +(Amount left, Amount right) => new(left.Value + right.Value); }

Example 2: another practical form

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using System.IO;
using System.Runtime.InteropServices;
using System.Runtime.CompilerServices;

public static class Program
{
    public static async Task Main(string[] args)
    {
        Counter value = new();
        value += 5; value++;
        Console.WriteLine(value.Value);
    }
}
public class Counter { public int Value { get; private set; } public void operator +=(int amount) { Value += amount; } public void operator ++() { Value++; } }

Example 3

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using System.IO;
using System.Runtime.InteropServices;
using System.Runtime.CompilerServices;

public static class Program
{
    public static async Task Main(string[] args)
    {
        Flag value = new(true);
        if (value) Console.WriteLine("Enabled");
    }
}
public readonly record struct Flag(bool Enabled) { public static bool operator true(Flag value) => value.Enabled; public static bool operator false(Flag value) => !value.Enabled; }

Official source: Microsoft Learn.