Comments on Programming and Debugging (in my Underhøøsen): The Power of Foreach

...please where can I buy a unicorn?

2009-11-21T21:36:48.508-08:00

...please where can I buy a unicorn?

BCSd, this is a great observation. I compiled an...

2009-06-25T19:12:08.262-07:00

BCSd, this is a great observation.

I compiled and tested the code snippets before posting, and they do work for the specific examples (where I break out of the foreach loops), but you are right: the correct implementation is for opApply to return the result of the delegate call.

And this just gives me some ideas for interesting test cases for my compiler back-end.

Thanks!

That is a nice overview of D's foreach system. Ho...

2009-06-25T10:28:46.886-07:00

That is a nice overview of D's foreach system.

However your code examples have one major flaw (I'm sure this is true in D1 but I think it is also true in D2):

The value returned by the delegate in opApply is not just a zero/non-zero value. The actual value is important. If the delegate returns a non-zero value, opApply MUST return that value or bazaar things start happening.

The easy way to implement this is:

if(auto ret = dg(val)) return ret;

The under the hood reason for this is that if the body of the delegate has more than one exit path (say a goto, a labeled break, a return, etc.) the foreach code detects which of these to do by examining the return value of opApply.