The util files are currently intertwined with the ntypes files through the Complex datatype, as sometimes we need to call Lua binding functions with either doubles or Complex!doubles. This also causes a duplication of some Lua bindings & functions. With the potential introduction of Dual numbers as an alternative adjoint computation method, this would introduce more duplication.

This merge proposes the use of limited templates, to remove the duplication, and allow for the util files to be decoupled from specific number types. The trait canCastTo is introduced, which allows compile-time checks if a type can be cast to another, either explicitly (using the cast(T) or to!(T) notation) or implicitly (by sub-typing). This is similar to the traits isFloating and isIntegral, however those cannot be extended to user-defined types.

public template canCastTo(T, U) {
    import std.traits : ReturnType;
    // Check if T can be implicitly or explicitly cast to U
    static if ( is(T : U) || is(ReturnType!(T.opCast!U) == U) ) {
        enum canCastTo = true;
    } else {
        enum canCastTo = false;
    }
}