Hello grauzone,
Jerry Quinn wrote:
Hi, all. I find myself a little confused about how foreach, opApply,
and delegates interact according to the docs.
Foreach on an aggregate will use the opApply call (assuming ranges
aren't being used). So if we use a simple example below, what
exactly is the delegate that is passed to opApply? The docs say a
delegate is a pairing of an object reference and a function, where
the object is passed as the 'this' parameter to the function. But
that doesn't seem to be the case here.
Is a virtual object with a function encompassing the body of the
foreach being silently created and passed in?
In one way of looking at it every stack frame is a virtual struct <g> so
yes, sort of.
The foreach body is like a nested function. Your example is (probably,
maybe this is wrong/oversimplified) compiled to something like this:
void foo() {
C c = new C;
int bla;
void something(uint v) {
bla = 123;
writefln(v);
}
c.opApply(&something);
}
IIRC if you compile with the -v flag you can even see DMD running code generation
for the foreach bodies.
(Although I think
it's perfectly fine to post this here, because the "gurus" don't post
and probably don't even read d.D.learn.)
I may not count as a "guru" but I'm "not a beginner" and do read it.
