"Delegate Constraint"

// Example from MSDN: https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/generics/constraints-on-type-parameters#delegate-constraints

public static TDelegate TypeSafeCombine<TDelegate>(this TDelegate source, TDelegate target)
    where TDelegate : System.Delegate
    => Delegate.Combine(source, target) as TDelegate;


Code snippet taken from "Two Decades of C#: A Reference - C# 7".