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digitalmars.D.bugs - [Issue 8338] New: Unqual doesn't work properly on arrays

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8338

           Summary: Unqual doesn't work properly on arrays
           Product: D
           Version: unspecified
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Phobos
        AssignedTo: nobody puremagic.com
        ReportedBy: jmdavisProg gmx.com


--- Comment #0 from Jonathan M Davis <jmdavisProg gmx.com> 2012-07-02 19:12:33
PDT ---
Take this bit of code

import std.stdio;
import std.traits;

void main()
{
    writeln(Unqual!(char[]).stringof);
    writeln(Unqual!(wchar[]).stringof);
    writeln(Unqual!(dchar[]).stringof);
    writeln(Unqual!(const char[]).stringof);
    writeln(Unqual!(const wchar[]).stringof);
    writeln(Unqual!(const dchar[]).stringof);
    writeln(Unqual!string.stringof);
    writeln(Unqual!wstring.stringof);
    writeln(Unqual!dstring.stringof);
    writeln();
    writeln(Unqual!(ubyte[]).stringof);
    writeln(Unqual!(short[]).stringof);
    writeln(Unqual!(uint[]).stringof);
    writeln(Unqual!(const ubyte[]).stringof);
    writeln(Unqual!(const short[]).stringof);
    writeln(Unqual!(const uint[]).stringof);
    writeln(Unqual!(immutable ubyte[]).stringof);
    writeln(Unqual!(immutable short[]).stringof);
    writeln(Unqual!(immutable uint[]).stringof);
}

It prints out

char[]
wchar[]
dchar[]
const(char)[]
const(wchar)[]
const(dchar)[]
string
immutable(wchar)[]
immutable(dchar)[]

ubyte[]
short[]
uint[]
const(ubyte)[]
const(short)[]
const(uint)[]
immutable(ubyte)[]
immutable(short)[]
immutable(uint)[]

None of those const or immutables should be there. The only changes between
this and not using Unqual at all is the const T[] are now const(T)[] and the
immutable T[] are now immutable(T)[]. And the immutable(T)[], are still
immutable(T)[]. The immutable on their elements aren't stripped.

Unqual specifically states that it removes _all_ qualifiers. It's clearly only
removing them from the array itself and not the elements, so it's not removing
all of the qualifiers.

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next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8338


Kenji Hara <k.hara.pg gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Version|unspecified                 |D2


--- Comment #1 from Kenji Hara <k.hara.pg gmail.com> 2012-07-02 19:40:39 PDT ---
(In reply to comment #0)

 Take this bit of code
 


[snip]

 
 None of those const or immutables should be there. The only changes between
 this and not using Unqual at all is the const T[] are now const(T)[] and the
 immutable T[] are now immutable(T)[]. And the immutable(T)[], are still
 immutable(T)[]. The immutable on their elements aren't stripped.
 
 Unqual specifically states that it removes _all_ qualifiers. It's clearly only
 removing them from the array itself and not the elements, so it's not removing
 all of the qualifiers.


Yes. std.traits.Unqual removes the top qualifier of given type, not all ones.
But, changing its implementation would break *maby* existing codes, so,
instead, we should fix its documentation.

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--- Comment #2 from Kenji Hara <k.hara.pg gmail.com> 2012-07-02 19:41:54 PDT ---

 But, changing its implementation would break *maby* existing codes, so,


s/maby/many/

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--- Comment #3 from Jonathan M Davis <jmdavisProg gmx.com> 2012-07-02 20:03:22
PDT ---
Maybe. But I'm not completely convinced that it would break all that much code
- particularly since I would have expected any code using Unqual to be written
with the intention of stripping _all_ of the qualifiers (as the documentation
says). If we don't make the change though, we need a new template similar to
Unqual (FullUnqual? RecUnqual?) which really _does_ strip all of the
qualifiers.

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--- Comment #4 from Kenji Hara <k.hara.pg gmail.com> 2012-07-02 21:01:13 PDT ---
(In reply to comment #3)

 Maybe. But I'm not completely convinced that it would break all that much code
 - particularly since I would have expected any code using Unqual to be written
 with the intention of stripping _all_ of the qualifiers (as the documentation
 says).


But, getting type stripped full qualifiers is much unsafe than just top.

  const string s = "Hello";   // const(immutable(char)[])
  auto mutable_s = cast(Unqual!(typeof(s)))s;  // ???

In many cases, current Unqual is used with unsafe casting, even if it is bad
idiom. Changing the implementation of Unqual will become such codes *more*
unsafe silently.
(As far as I know, Phobos doesn't have such bad using. I'm talking about the
user codes written by programmers don't know well about const/immutable type
system.)

And in (sadly) few cases that uses Unqual correct way, it will change codes
from safe to unsafe.

  Stripping top qualifier of array/string types:
 
https://github.com/D-Programming-Language/phobos/blob/master/std/format.d#L1634
 
https://github.com/D-Programming-Language/phobos/blob/master/std/format.d#L1705



 If we don't make the change though, we need a new template similar to
 Unqual (FullUnqual? RecUnqual?) which really _does_ strip all of the
 qualifiers.


Noqual?

Or, add new two templates, one removes just top qualifier, another does all
qualifiers. I think this is the best way, but have no idea about their names...

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