EN CSharp Keyword interface

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C#: interface

Handbook C# · Practical Guide

Declares a type contract. Supports instance members, default implementations, and static abstract members.

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
ILabel item = new Item();
System.Console.WriteLine(item.Label);
interface ILabel { string Label { get; } }
class Item : ILabel { public string Label => "Ore"; }

Result:

Ore

Syntax

interface IName { ... }

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)
    {
        Entity entity = new Player("Archer");
        Console.WriteLine(entity.Describe());
        Console.WriteLine(entity.Code);
    }
}
public interface ILabel { string Label { get; } }
public abstract class Entity : ILabel
{
    private readonly string name;
    protected Entity(string name) { this.name = name; }
    protected string Name => name;
    internal int Code { get; set; } = 7;
    public virtual string Label => Name;
    public abstract string Describe();
}
public sealed class Player : Entity
{
    public Player(string name) : base(name) { }
    public override string Label => "Player: " + base.Label;
    public override string Describe() => Label;
}

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)
    {
        Console.WriteLine(MathFactory.Get<Number>());
    }
}
public interface IValue<T> where T : IValue<T> { static abstract int Value { get; } }
public struct Number : IValue<Number> { public static int Value => 12; }
public static class MathFactory { public static int Get<T>() where T : IValue<T> => T.Value; }

Official source: Microsoft Learn.