Hi, Walter and Sean.

It looks like the foreach aggregate is using a lamda like function to do the loop, this is very much like std::for_each in C++.

But std::for_each cannot handle break, return because the loop body is a functor. Neither can regular functional language construct like foldl.

But how does foreach in D handle this?

It's easy for arrays. But when an apply method is called, how does a break exit from the apply method? Is it a special exception?

Ben.

In article <bnbj91$24ki$1@digitaldaemon.com>, Ben Y. says...
>
>Hi, Walter and Sean.
>
>It looks like the foreach aggregate is using a lamda like function to do the loop, this is very much like std::for_each in C++.
>
>But std::for_each cannot handle break, return because the loop body is a functor. Neither can regular functional language construct like foldl.
>
>But how does foreach in D handle this?
>
>It's easy for arrays. But when an apply method is called, how does a break exit from the apply method? Is it a special exception?
>
>Ben.

Look at the foreach documentation here http://www.digitalmars.com/d/statement.html#foreach

The delegate generated for the foreach body will return a non zero
value when it encounters a break.  I'm not sure what happens with a return.

<quote>
The body of the apply  function iterates over the elements it aggregates,
passing them each to the dg function. If the dg returns 0, then apply goes on to
the next element. If the dg returns a nonzero value, apply must cease iterating
and return that value. Otherwise, after done iterating across all the elements,
apply will return 0.
</quote>

"Patrick Down" <Patrick_member@pathlink.com> wrote in message news:bnbtrs$2iud$1@digitaldaemon.com...
> Look at the foreach documentation here http://www.digitalmars.com/d/statement.html#foreach
>
> The delegate generated for the foreach body will return a non zero value when it encounters a break.  I'm not sure what happens with a
return.
>
> <quote>
> The body of the apply  function iterates over the elements it aggregates,
> passing them each to the dg function. If the dg returns 0, then apply goes
on to
> the next element. If the dg returns a nonzero value, apply must cease
iterating
> and return that value. Otherwise, after done iterating across all the
elements,
> apply will return 0.
> </quote>

Try various kinds of break, continue, return, and goto's out of a foreach body. You'll see that each is replaced with a return value, and there's a switch statement on these values automagically generated by the compiler to replace the foreach statement.

>Try various kinds of break, continue, return, and goto's out of a foreach body. You'll see that each is replaced with a return value, and there's a switch statement on these values automagically generated by the compiler to replace the foreach statement.
>
>
I can understand that "return;" can be handled with a special return value. But what about "return someStruct;"? How does the return value get passed from the delegate to the apply function then to the calling function?

"Ben Y." <Ben_member@pathlink.com> wrote in message news:bnc3ec$2qcd$1@digitaldaemon.com...
>
> >Try various kinds of break, continue, return, and goto's out of a foreach body. You'll see that each is replaced with a return value, and there's a switch statement on these values automagically generated by the compiler
to
> >replace the foreach statement.
> I can understand that "return;" can be handled with a special return
value. But
> what about "return someStruct;"? How does the return value get passed from
the
> delegate to the apply function then to the calling function?

The easiest way to see how this works is to write a simple test program, compile it, and obj2asm it. It works generally like nested local variable access.