On Thursday, 5 March 2020 at 14:24:33 UTC, wjoe wrote:
Implement this for free functions i would do something like this
void dispatch(alias fn, ARGS...)(Handle handle, ARGS args)
Why do you need an `alias fn` like that?
My suggestion would be to just use the `opDispatch` magic method
that gives you a string, then `__traits(getMember, obj,
memberName)(args)` to call it.
But if you specifically need the alias param that won't work as
well. (You could still do `__traits(getMember, obj,
__traits(identifier, fn))` though, so it isn't ruled out
entirely, just not as nice. That is also more likely to break
with overloads btw)
struct Handle {
private Whatever obj;
auto opDispatch(string name, Args...)(Args args) {
return __traits(getMember, obj, name)(args);
}
}
And the usage would look like:
auto size = f.getSize(wallpaperhandle);
assuming the Handle knows how to store Whatever without being
told what it is again at the call site (e.g. if you actually use
an `interface` internally, or an encapsulated tagged union or
whatever).
If you do need to tell it what it is, a two-level function gives
that opportunity:
template opDispatch(string name) {
auto opDispatch(T, Args...)(Args args) {
auto obj = cast(T) o; // or whatever you do to convert
return __traits(getMember, obj, name)(args);
}
}
then the usage looks like
auto size = f.getSize!Bitmap(wallpaperhandle);
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.
But it depends on what exactly you are doing.
