C# 14 - Extension Members 🚀

C# 14 adds new syntax to define extension members. The new syntax enables you to declare extension properties in addition to extension methods. ✔️

You can also declare extension members that extend the type, rather than an instance of the type. In other words, these new extension members can appear as static members of the type you extend.

The following code example shows an example of the different kinds of extension members you can declare:

public static class Enumerable
{
    // Extension block
    extension<TSource>(IEnumerable<TSource> source) // extension members for IEnumerable<TSource>
    {
        // Extension property:
        public bool IsEmpty => !source.Any();
        // Extension indexer:
        public TSource this[int index] => source.Skip(index).First();

        // Extension method:
        public IEnumerable<TSource> Where(Func<TSource, bool> predicate) { ... }
    }

    // extension block, with a receiver type only
    extension<TSource>(IEnumerable<TSource>) // static extension members for IEnumerable<Source>
    {
        // static extension method:
        public static IEnumerable<TSource> Combine(IEnumerable<TSource> first, IEnumerable<TSource> second) { ... }

        // static extension property:
        public static IEnumerable<TSource> Identity => yield return default;
    }
}

The members in the first extension block are called as though they're instance members of IEnumerable<TSource>, for example sequence.IsEmpty. The members in the second extension block are called as though they're static members of IEnumerable<TSource>, for example IEnumerable<int>.Identity.


[ Blog ] : https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/extension-methods

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