question about foreach, opApply, and delegates

[BCS]

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.