why a method has to be generic when passing a generic type

Question

For example i have this C# method :

public static int Count<T>(IEnumerable<T> sequence)
{         
     return 0;
}

Why i have to write Count<T> rather than Count even when i'm not using the T type inside the method ?

Answer 1

You don't have to. You could go entirely non-generic:

public static int Count(IEnumerable sequence)
{         
     return 0;
}

And since IEnumerable<out T> : IEnumerable , this will work for all sequences.

One reason not to do this, however, is that if you plan to do:

int count = 0;
foreach(var obj in sequence) count++;
return count;

then the non-generic version when used with value types will box every value - increasing allocations. The generic version will not do any boxing.