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digitalmars.D.bugs - [Issue 2571] New: const static arrays: const(T)[N] and const(T[N]) are the same, but DMD treats them as different

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http://d.puremagic.com/issues/show_bug.cgi?id=2571

           Summary: const static arrays: const(T)[N] and const(T[N]) are the
                    same, but DMD treats them as different
           Product: D
           Version: 2.023
          Platform: PC
        OS/Version: Windows
            Status: NEW
          Keywords: rejects-valid, wrong-code
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: bugzilla digitalmars.com
        ReportedBy: smjg iname.com


You can apply const to the whole of a static array type or to the element type
thereof.  Since static arrays have value semantics, the result is the same: you
can neither change an element in the array nor reassign to it a whole new
array.  Nonetheless, DMD treats them as different types:

----- const_static_array_1.d -----
const(char)[26] abc1 = "abcdefghijklmnopqrstuvwxyz";
const(char[26]) abc2 = "abcdefghijklmnopqrstuvwxyz";

pragma(msg, typeof(abc1).stringof);
pragma(msg, typeof(abc2).stringof);
pragma(msg, (const(char)[26]).stringof);
pragma(msg, (const(char[26])).stringof);

pragma(msg, is(typeof(abc1) : typeof(abc2)).stringof);
pragma(msg, is(typeof(abc2) : typeof(abc1)).stringof);
pragma(msg, is(typeof(abc1) == typeof(abc2)).stringof);
----------
C:\Users\Stewart\Documents\Programming\D\d2\tests>dmd -c const_static_array_1.d
const(char)[26u]
const(char[26u])
const(char)[26u]
const(char[26u])
true
true
false
----------

Moreover, while they are implicitly convertible, that they are treated as
different types creates a silly template incompatibility:
----- const_static_array_2.d -----
const(char)[26] abc1 = "abcdefghijklmnopqrstuvwxyz";
const(char[26]) abc2 = "abcdefghijklmnopqrstuvwxyz";

class Temp(T) {}

void main() {
    Temp!(const(char)[26]) t1;
    Temp!(const(char[26])) t2;

    t1 = t2;
    t2 = t1;
}
----------
C:\Users\Stewart\Documents\Programming\D\d2\tests>dmd const_static_array_2.d
const_static_array_2.d(10): Error: cannot implicitly convert expression (t2) of
type const_static_array_2.Temp!(const(char[26u])).Temp to
const_static_array_2.Temp!(const(char)[26u]).Temp
const_static_array_2.d(11): Error: cannot implicitly convert expression (t1) of
type const_static_array_2.Temp!(const(char)[26u]).Temp to
const_static_array_2.Temp!(const(char[26u])).Temp
----------


-- 
Jan 10 2009
next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=2571


smjg iname.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|const static arrays:        |const/invariant/immutable
                   |const(T)[N] and const(T[N]) |static arrays: const(T)[N]
                   |are the same, but DMD treats|and const(T[N]) are the
                   |them as different           |same, but DMD treats them as
                   |                            |different




------- Comment #1 from smjg iname.com  2009-01-10 10:48 -------
The type should be reported as const(char[26]) in either case.  And here's
another case of the same basic bug:

----------
invariant(const(char)[26]) abc1 = "abcdefghijklmnopqrstuvwxyz";
const(invariant(char)[26]) abc2 = "abcdefghijklmnopqrstuvwxyz";

pragma(msg, typeof(abc1).stringof);
pragma(msg, typeof(abc2).stringof);
pragma(msg, (invariant(const(char)[26])).stringof);
pragma(msg, (const(invariant(char)[26])).stringof);

pragma(msg, is(typeof(abc1) : typeof(abc2)).stringof);
pragma(msg, is(typeof(abc2) : typeof(abc1)).stringof);
pragma(msg, is(typeof(abc1) == typeof(abc2)).stringof);
----------
C:\Users\Stewart\Documents\Programming\D\d2\tests>dmd -c const_static_array_3.d
immutable(char[26u])
const(immutable(char)[26u])
immutable(char[26u])
const(immutable(char)[26u])
true
true
false
----------
Again, the two should denote the exact same type, invariant(char[26u]). 
(immutable?  invariant?  See also issue 2572.)


-- 
Jan 10 2009
prev sibling next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=2571



--- Comment #2 from Stewart Gordon <smjg iname.com> 2010-06-24 17:49:56 PDT ---
Created an attachment (id=675)
Example of a squashed summary line

Rendered by Firefox 3.6.3 at inner width 1000.  If you make it much narrower,
you get a horizontal scrollbar.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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Stewart Gordon <smjg iname.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
 Attachment #675 is|0                           |1
           obsolete|                            |


--- Comment #3 from Stewart Gordon <smjg iname.com> 2010-06-24 17:52:10 PDT ---
(From update of attachment 675)
Sorry, attached to wrong bug report.  Reposted on issue 4386.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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Walter Bright <bugzilla digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bugzilla digitalmars.com


--- Comment #4 from Walter Bright <bugzilla digitalmars.com> 2010-11-07
14:29:20 PST ---
You're right, this is a bit of a mess and should be fixed.

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Nov 07 2010
prev sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=2571


Walter Bright <bugzilla digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED


--- Comment #5 from Walter Bright <bugzilla digitalmars.com> 2010-11-07
20:42:55 PST ---
http://www.dsource.org/projects/dmd/changeset/744

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