On Thursday, 25 December 2014 at 15:50:07 UTC, Danny wrote:
struct X {
int a;
}
class Foo {
X value;
template opDispatch(string s) {
value.opDispatch!(s) opDispatch;
That won't work anyway since X doesn't implement opDispatch - it
needs to be written in the function by the user to be used.
opDispatch is a function called when a member isn't found. So
with yours:
Foo.value -> value is found, so opDispatch is never called.
Foo.a -> value not found, the compiler tries Foo.opDispatch!"a".
If that compiles, it works. Otherwise, it issues the "has no
property" error.
A few tips with opDispatch:
* since you just get "no such property" if it fails, you don't
know *why* it failed. To get a better error message when you know
it should be working but isn't, try writing it out yourself:
foo.opDispatch!"a";
and the compiler will give you more information about why it
didn't work.
* opDispatch is often a function. It doesn't have to be, but it
usually is:
auto opDispatch(string name)() {
return something;
}
Is there another way to make Foo forward all unknown things to
X ?
You could try writing:
auto opDispatch(string name)() {
return mixin("value." ~ name);
}
That would do it.
There is also alias this and opDot that does forwarding. I can't
find the docs for them right now but add "alias value this;" to
your class for one option or.... I think "X* opDot() { return
&value; }" for the other.
alias this forwards any unknown properties to another member and
also allows implicit conversion. It is kinda like how inheritance
from a base class works.
opDot is an older function that might be removed at some point,
it predates opDispatch and alias this, but what it does is
forward to a return value when it isn't found.
