[Issue 11934] Allow `ref` in `foreach` over range iff `front` returns by `ref`

Aug 08, 2016

Ketmar Dark

Dec 19, 2017

Nick Treleaven

Jun 14, 2018

Jun 14, 2018

Feb 21, 2019

Feb 25, 2019

Mar 01, 2019

Aug 19

Aug 19

Aug 19

https://issues.dlang.org/show_bug.cgi?id=11934 Ketmar Dark <ketmar@ketmar.no-ip.org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |ketmar@ketmar.no-ip.org --

https://issues.dlang.org/show_bug.cgi?id=11934 Nick Treleaven <nick@geany.org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |nick@geany.org See Also| |https://issues.dlang.org/sh | |ow_bug.cgi?id=11935 --

https://issues.dlang.org/show_bug.cgi?id=11934 Richard Cattermole <alphaglosined@gmail.com> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |alphaglosined@gmail.com --- Comment #2 from Richard Cattermole <alphaglosined@gmail.com> --- A more substantial example of why this is a problem: --- import std.stdio; import std.algorithm; struct A { this(int i) { id=counter++; counterLive[id] = 1; writeln("CTOR ", id); } ~this() { counterLive[id]--; writeln("DTOR ", id); } this(this) { counterLive[id]++;writeln("POSTBLIT ", id); } static size_t counter=1; static size_t[size_t] counterLive; size_t id; } void main() { foreach(ref r; [A(10), A(2), A(3)].map!(x => x)) { } foreach(k, v; A.counterLive) if (v > 0) writeln("A (", k, ") count ", v); } --- Output: --- CTOR 1 CTOR 2 CTOR 3 POSTBLIT 1 POSTBLIT 1 DTOR 1 POSTBLIT 2 POSTBLIT 2 DTOR 2 POSTBLIT 3 POSTBLIT 3 DTOR 3 A (2) count 2 A (3) count 2 A (1) count 2 DTOR 3 DTOR 2 DTOR 1 --- The destructors for 3 copies never get called. --

February 21, 2019

[Issue 11934] Allow `ref` in `foreach` over range iff `front` returns by `ref`

Posted by Simen Kjaeraas

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Simen Kjaeraas

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https://issues.dlang.org/show_bug.cgi?id=11934

Simen Kjaeraas <simen.kjaras@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |simen.kjaras@gmail.com

--- Comment #3 from Simen Kjaeraas <simen.kjaras@gmail.com> ---
Simplified example:

import std.stdio;
import std.algorithm;

struct A {
    this(int i) { writeln("ctor ", &this); }
    ~this() { writeln("dtor ", &this); }
    this(this) { writeln("postblit ", &this); }
}

unittest {
    writeln("Without ref:");
    foreach(r; [1].map!(x => A(x))) { }
    writeln("With ref:");
    foreach(ref r; [1].map!(x => A(x))) { }
}

As we can see from the output, the dtor is correctly called in the non-ref case, but not in the ref case. Memory addresses are the same in both cases, and are stack addresses, so it's not a case of 'allocate on heap and let GC sort it out'.

As Denis points out though, it may be better for this not to compile than to compile and silently do something other than expected (even though the ref'ed struct is mutated, this is not reflected anywhere since it's a temporary).

--

https://issues.dlang.org/show_bug.cgi?id=11934 Dlang Bot <dlang-bot@dlang.rocks> changed: What |Removed |Added ---------------------------------------------------------------------------- Keywords| |pull --- Comment #4 from Dlang Bot <dlang-bot@dlang.rocks> --- @trikko updated dlang/dmd pull request #8437 "Fixed issue 11934. Range with a non-ref front + foreach(ref...)" fixing this issue: - Fixed issue 11934. Range with a non-ref front + foreach(ref...) https://github.com/dlang/dmd/pull/8437 --

https://issues.dlang.org/show_bug.cgi?id=11934 Dlang Bot <dlang-bot@dlang.rocks> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|NEW |RESOLVED Resolution|--- |FIXED --- Comment #5 from Dlang Bot <dlang-bot@dlang.rocks> --- dlang/dmd pull request #8437 "Fixed issue 11934. Range with a non-ref front + foreach(ref...)" was merged into master: - 9a9bcb0cd78dda7ef0c6da0444e10af5b67cfa65 by Andrea Fontana: Fixed issue 11934. Range with a non-ref front + foreach(ref...) https://github.com/dlang/dmd/pull/8437 --

https://issues.dlang.org/show_bug.cgi?id=11934 Nick Treleaven <nick@geany.org> changed: What |Removed |Added ---------------------------------------------------------------------------- See Also| |https://issues.dlang.org/sh | |ow_bug.cgi?id=24679 --

https://issues.dlang.org/show_bug.cgi?id=11934 --- Comment #6 from Nick Treleaven <nick@geany.org> --- (In reply to Denis Shelomovskii from comment #0) > static assert(!__traits(compiles, { foreach(ref n; S1()) { } })); // fails This line still fails, so reopening. This could be fixed in the next edition. --

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