The in operator (along with other things) is designed poorly.

[Adam D Ruppe]

On Tuesday, 31 May 2022 at 00:16:46 UTC, Ruby The Roobster wrote:
>     static if(0 in [0: 0]) //This expression should be true.

You can check the pointer it returns for null.

      static if((0 in [0: 0]) !is null)


> __traits(getOverloads, ... , ... ).

Notice the third argument described in the docs:

https://dlang.org/spec/traits.html#getOverloads

Reflection over templates is underpowered but there is a thing 
there to get the template overloads.