struct SList {

    this(T)(int n, T alloc) {}

​

} 

struct DList {

    this(T)(int n, T alloc) {}

} 

​

struct WithAlloc(alias alloc)

{

    auto opDispatch(string s, Args...)(auto ref Args args)

        if (__traits(compiles, mixin(s ~ "(args, alloc)")))

    {

        mixin("return " ~ s ~ "(args, alloc);");

    }

}

​

struct DumbAlloc { }

​

void main() {

    auto alloc = new DumbAlloc;

    auto withAlloc = WithAlloc!(alloc)();

    auto slist = withAlloc.SList(0);

    auto dlist = withAlloc.DList(0); 

}