import std.stdio;

​

template Nullable(S)

{

    import std.traits : isPointer, isDynamicArray;

    static if (is(S == class) || is(S == interface)

               || is(S == function) || is(S == delegate)

               || isPointer!S || isDynamicArray!S)

    {

        alias Nullable = S;

    }

    else

    {

        static import std.typecons;

        alias Nullable = std.typecons.Nullable!S;

    }

}

​

struct S

{

    Nullable!Object s;

}

​

void main()

{

    S s;

    writeln(s.s is null);

}