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digitalmars.D.bugs - [Issue 5163] New: meaningless error message with front() applied to void[]

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=5163

           Summary: meaningless error message with front() applied to
                    void[]
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Keywords: diagnostic, rejects-valid
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: mrmocool gmx.de


--- Comment #0 from Trass3r <mrmocool gmx.de> 2010-11-04 08:08:33 PDT ---
import std.array;
void main()
{
    void[] a = cast(void[]) [ 1, 2, 3 ];
    a.front;
}

yields:
..\src\phobos\std\array.d(419): Error: [i] has no effect in expression (a[0u])
..\src\phobos\std\array.d(5): Error: template instance std.array.front!(void[])
error instantiating

Originally I used std.file.read(), hence the void array.

- 1st message is completely senseless, what "[i]"?
- 2nd message shows line 5 which is the line of "a.front;" but the filename is
wrong.

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next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=5163


Lars T. Kyllingstad <bugzilla kyllingen.net> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bugzilla kyllingen.net
          Component|DMD                         |Phobos


--- Comment #1 from Lars T. Kyllingstad <bugzilla kyllingen.net> 2010-11-05
04:38:32 PDT ---
This is actually two separate issues.

The first is a Phobos issue, namely that there should be a template constraint
on std.array.front() that prevents it from being instantiated on void[] arrays.
 front() is defined as something like

    T front(T)(T[] array) { return array[0]; }

You cannot index into a void[] array, hence the first error message.  This also
means that void[] cannot be a range.

The second is the issue of the wrong line number, which is a bug in DMD. I'm
guessing it's just bug 1913 again, so I'm marking this one as a Phobos issue.


In the case of a void[] returned from std.file.read(), you need to cast it to
ubyte[] before using it as a range.

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Nov 05 2010
prev sibling next sibling parent d-bugmail puremagic.com writes:
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Lars T. Kyllingstad <bugzilla kyllingen.net> changed:

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


--- Comment #2 from Lars T. Kyllingstad <bugzilla kyllingen.net> 2010-11-05
05:18:35 PDT ---
This fixes the Phobos bug:
http://www.dsource.org/projects/phobos/changeset/2123

The error message is now:
test.d(6): Error: template std.array.front(A) if (is(typeof(A[0])) &&
!isNarrowString!(A) && !is(typeof(A[0]) : const(void))) does not match any
function template declaration
test.d(6): Error: template std.array.front(A) if (is(typeof(A[0])) &&
!isNarrowString!(A) && !is(typeof(A[0]) : const(void))) cannot deduce template
function from argument types !()(void[])

Arguably less readable, but more useful since it refers to the point of error
in user code instead of in Phobos code.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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bearophile_hugs eml.cc changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bearophile_hugs eml.cc


--- Comment #3 from bearophile_hugs eml.cc 2010-11-05 05:36:36 PDT ---
(In reply to comment #2)

 Arguably less readable, but more useful since it refers to the point of error
 in user code instead of in Phobos code.
Too bad there is no handy way to add error messages to template constraints... -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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--- Comment #4 from Trass3r <mrmocool gmx.de> 2010-11-05 09:37:28 PDT ---
Thx for the fix, but I still think that strange [i] in the error message is a
diagnostic bug, reopen it?

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prev sibling parent d-bugmail puremagic.com writes:
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Lars T. Kyllingstad <bugzilla kyllingen.net> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|rejects-valid               |


--- Comment #5 from Lars T. Kyllingstad <bugzilla kyllingen.net> 2010-11-08
02:26:24 PST ---
I think '[i]' is just a compact way of saying 'indexing operation'.  I guess it
could just as well have been '[#]', '[index]', or whatever.  (Even better would
be a message saying that you can't index into void[] arrays.)

Anyway, I suggest you open a new bug report about it.  It's better not to have
two bugs in one report -- especially when one is a Phobos bug and the other is
a DMD bug.

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