[Issue 17771] foreach over const input range fails (page 2)

https://issues.dlang.org/show_bug.cgi?id=17771 ag0aep6g@gmail.com changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |ag0aep6g@gmail.com --- Comment #11 from ag0aep6g@gmail.com --- (In reply to Alex Goltman from comment #9) > the error stating foreach doesn't work with a > const actually made me question whether foreach over a range modifies the > range I give it, I don't really have a horse in this race, but if we consider a generic range, then `foreach` does very much modify it. `foreach` doesn't call `save`, so every `popFront` potentially modifies the original range. It doesn't really matter that `foreach` copies the range, because copying is not a range concept. If you have a generic range, and you run it through `foreach`, you must be prepared to have an empty range afterwards. --

August 22, 2017

[Issue 17771] foreach over const input range fails

Posted by Jonathan M Davis

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Jonathan M Davis

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https://issues.dlang.org/show_bug.cgi?id=17771

Jonathan M Davis <issues.dlang@jmdavisProg.com> changed:

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--- Comment #12 from Jonathan M Davis <issues.dlang@jmdavisProg.com> ---
For const to work with ranges, we'd really need some sort of tail-const slicing mechanism similar to what happens with dynamic arrays and IFTI (though presumably, it would require help from the programmer as opposed to being automatic, since it really can't be done automatically with ranges like it can be with arrays). But wthout some form of tail-const mechanism, it's a waste of time to muck around with const and ranges. Best case, you make certain use cases work while having a bunch that don't. At this point, it's far better to just never use const with ranges. They're pretty much inherently incompatible given the fact that iterating a range modifies it, and the only defined way to copy a range is save. Technically, even using a range after passing it to a function or using foreach on it is undefined behavior in generic code, since the copy semantics differ wildly depending on how the range is defined. So, trying to do anything with const automatically is a total minefield. My answer to anyone trying to use const with ranges is to just give up now. They simply don't work together, and trying to make them work together without language additions related to tail-const is just going to cause you grief in the long run.

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https://issues.dlang.org/show_bug.cgi?id=17771 Paul Backus <snarwin+bugzilla@gmail.com> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |elpenguino+D@gmail.com --- Comment #13 from Paul Backus <snarwin+bugzilla@gmail.com> --- *** Issue 18631 has been marked as a duplicate of this issue. *** --

https://issues.dlang.org/show_bug.cgi?id=17771 Iain Buclaw <ibuclaw@gdcproject.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Priority|P1 |P4 --

https://issues.dlang.org/show_bug.cgi?id=17771 --- Comment #14 from dlangBugzillaToGithub <robert.schadek@posteo.de> --- THIS ISSUE HAS BEEN MOVED TO GITHUB https://github.com/dlang/dmd/issues/19308 DO NOT COMMENT HERE ANYMORE, NOBODY WILL SEE IT, THIS ISSUE HAS BEEN MOVED TO GITHUB --

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