How to dispatch a class function for an object accessed by handle?

[wjoe]

On Thursday, 5 March 2020 at 18:33:41 UTC, Adam D. Ruppe wrote:
> On Thursday, 5 March 2020 at 14:24:33 UTC, wjoe wrote:
>
> [...]
>
> template opDispatch(string name) {
>     auto opDispatch(T, Args...)(Args args) {
>        ...
>     }
> }
>
> [...]
>
>
> NOTE: opDispatch suppresses internal compile errors, it will 
> just say "no such property whatever". you can explicitly 
> instantiate with `f.opDispatch!"whatever` to help see better 
> errors.
>

Follow-up question:

Calling f.whatever!SomeResource(...); works no problem.
However I can't figure out how to call a function by explicitly 
instantiating opDispatch.

Since f.opDispatch!"load"(handle, "wallpaper.png");
doesn't compile, I refreshed my memory about the shortcut syntax 
and the eponymous syntax and the way I read it is that this is a 
template of a template.

So I tried this: f.opDispatch!"load".opDispatch!Bitmap(handle, 
"path/to/wallpaper.png");

But this doesn't compile either and errors out with:
Error: Cannot resolve type for f.opDispatch(T, 
ARGS...)(ResourceHandle handle, ARGS args)

I don't understand this error message. Which type can't be 
resolved?

Is there a way to look at output of what the compiler generates 
for f.whatever!SomeResource(...); ?