[Issue 3567] std.traits: Unqual doesn't handle arrays well

[Issue 3567] std.traits: Unqual strips qualifiers on structs with references that would break const/immutable.

Jul 12, 2018

Steven Schveighoffer

Jul 12, 2018

Jul 12, 2018

Jul 12, 2018

Dec 12, 2019

Dec 01

dlangBugzillaToGithub

https://issues.dlang.org/show_bug.cgi?id=3567 Andrei Alexandrescu <andrei@erdani.com> changed: What |Removed |Added ---------------------------------------------------------------------------- Version|2.036 |D2 --

https://issues.dlang.org/show_bug.cgi?id=3567 FeepingCreature <default_357-line@yahoo.de> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|RESOLVED |REOPENED CC| |default_357-line@yahoo.de Resolution|INVALID |--- --- Comment #3 from FeepingCreature <default_357-line@yahoo.de> --- This bug needs a second look. Consider this code: struct S { int* ipointer; } pragma(msg, (Unqual!(const S)).stringof); As can be seen, Unqual has just deeply stripped const, not shallowly. Either Unqual must be made to error when passed a const struct with reference, or Unqual must leave const(int[]) as int[]. The current state is broken. --

https://issues.dlang.org/show_bug.cgi?id=3567 Steven Schveighoffer <schveiguy@yahoo.com> changed: What |Removed |Added ---------------------------------------------------------------------------- Keywords| |safe CC| |schveiguy@yahoo.com Hardware|Other |All OS|Linux |All Severity|normal |major --- Comment #4 from Steven Schveighoffer <schveiguy@yahoo.com> --- This is likely going to be disruptive to fix, so many things use Unqual. But nonetheless, it's an important bug. --

July 12, 2018

[Issue 3567] std.traits: Unqual doesn't handle arrays well

Posted by Timoses

Permalink

Timoses

Permalink

https://issues.dlang.org/show_bug.cgi?id=3567

Timoses <timosesu@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |timosesu@gmail.com

--- Comment #5 from Timoses <timosesu@gmail.com> ---
The fact the Unqual only "shallowly" unqualifies a type can be pretty annoying when dealing with templates and inout functions.


struct S
{
    int[] vals;
}

template Temp(T)
{
    class Temp
    {
        T t;

        this(T t)
        { this.t = t; }

        auto get() inout
        {
            static if (is(T == S))
            {
                import std.traits : Unqual;
                alias tType = Unqual!(typeof(t.vals));
                pragma(msg, tType); // inout(int)[]
                return new inout Temp!tType(t.vals); // ERROR: Can't create
class Temp!(inout(int)[])
            }
        }
    }
}

unittest
{
    auto t = Temp!S;
    t.get();
}

Error: variable `onlineapp.Temp!(inout(int)[]).Temp.t` only parameters or stack
based variables can be inout
Error: template instance `onlineapp.Temp!(inout(int)[])` error instantiating


In this case a complete stripping of qualifiers is required!

Related discussion: https://forum.dlang.org/post/enwkjtdqivjldqpzzqrw@forum.dlang.org

--

https://issues.dlang.org/show_bug.cgi?id=3567 Steven Schveighoffer <schveiguy@yahoo.com> changed: What |Removed |Added ---------------------------------------------------------------------------- Summary|std.traits: Unqual doesn't |std.traits: Unqual strips |handle arrays well |qualifiers on structs with | |references that would break | |const/immutable. --- Comment #6 from Steven Schveighoffer <schveiguy@yahoo.com> --- Note, the bug here in FeepingCreature's case is that it strips more than it should. It is supposed to be safe to use Unqual. So the expectation that Unqual should remove all mutability modifiers is incorrect. I'm changing the title accordingly. Perhaps we should actually close this bug and open another, as the whole issue has really been flipped around? --

https://issues.dlang.org/show_bug.cgi?id=3567 --- Comment #7 from Timoses <timosesu@gmail.com> --- (In reply to Steven Schveighoffer from comment #6) > I'm changing the title accordingly. Perhaps we should actually close this bug and open another, as the whole issue has really been flipped around? Perhaps you're looking for this? https://issues.dlang.org/show_bug.cgi?id=8338 --

https://issues.dlang.org/show_bug.cgi?id=3567 --- Comment #8 from Timoses <timosesu@gmail.com> --- (In reply to Steven Schveighoffer from comment #6) > Note, the bug here in FeepingCreature's case is that it strips more than it should. It is supposed to be safe to use Unqual. > > So the expectation that Unqual should remove all mutability modifiers is incorrect. Tried to find examples where a complete stripping of qualifiers would break something. I guess here it is really required that it only strips the "head" qualifier: https://github.com/dlang/phobos/blob/90a8fc387f25f9bdfc2c6ad4508da63c523be670/std/array.d#L1465 Though this is not the subject of this issue.. Should I perhaps create a new issue for https://issues.dlang.org/show_bug.cgi?id=3567#c5 ? Perhaps asking for a new trait? --

https://issues.dlang.org/show_bug.cgi?id=3567 --- Comment #9 from Steven Schveighoffer <schveiguy@yahoo.com> --- I think a trait "ForceUnqual" may be needed in some cases, but "Unqual" I have always expected to behave the way it does (except in the case of structs containing references, for which it should not strip anything). Man, it would be nice to have a tail-modifier in D... --

https://issues.dlang.org/show_bug.cgi?id=3567 berni44 <bugzilla@d-ecke.de> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |issues.dlang@jmdavisProg.co | |m --- Comment #10 from berni44 <bugzilla@d-ecke.de> --- *** Issue 8338 has been marked as a duplicate of this issue. *** --

https://issues.dlang.org/show_bug.cgi?id=3567 --- Comment #11 from dlangBugzillaToGithub <robert.schadek@posteo.de> --- THIS ISSUE HAS BEEN MOVED TO GITHUB https://github.com/dlang/phobos/issues/9805 DO NOT COMMENT HERE ANYMORE, NOBODY WILL SEE IT, THIS ISSUE HAS BEEN MOVED TO GITHUB --

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