http://d.puremagic.com/issues/show_bug.cgi?id=2486

           Summary: taking address of slice rvalue is valid
           Product: D
           Version: 1.037
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Keywords: spec
          Severity: minor
          Priority: P2
         Component: DMD
        AssignedTo: bugzilla@digitalmars.com
        ReportedBy: kamm-removethis@incasoftware.de


I was surprised to see that following compiles and generates reasonable code:

int[] a = [1, 2, 3]
auto addr = &a[0..2];

Since the frontend seems to explicitly allow it, it's probably intentional and we've made LDC behave the same way. Could a description and rationale be added to the spec?


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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Platform|x86                         |All
            Version|1.037                       |D1 & D2
         OS/Version|Linux                       |All
           Severity|minor                       |normal


--- Comment #1 from Kenji Hara <k.hara.pg@gmail.com> 2011-11-10 03:09:27 PST ---
This is still valid in D2.

import std.stdio;
void main()
{
    int[] arr = [1,2,3];
    auto p = &(arr[0..2]);  // same as &(arr[0..2])
    writeln(typeof(p).stringof);    // int[]*
    writeln(arr.ptr);
    writeln(&arr);
    writeln(p);
    assert(&arr == p);
}

I think this is bad behavior, because it allows nonsense code like follows.

void main()
{
    int[] arr = [1,2,3];
    foo(arr[0..2]);         // ref parameter can receive lvalue made by slicing
    assert(arr == [1,2,3]); // assertion succeeds...
}
void foo(ref int[] arr)
{
    arr = [4,5,6];          // what is modified?
}

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Walter Bright <bugzilla@digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|spec                        |
                 CC|                            |bugzilla@digitalmars.com


--- Comment #2 from Walter Bright <bugzilla@digitalmars.com> 2012-01-22 20:13:33 PST ---
I agree, and will fix the spec. So it's a compiler bug that this code is accepted. It should only work for const references. Changing to a compiler bug.

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--- Comment #3 from Kenji Hara <k.hara.pg@gmail.com> 2012-01-24 05:38:49 PST ---
Maybe the documentation fix is:

https://github.com/D-Programming-Language/d-programming-language.org/commit/8681d6fb36bd7a00a395bfc66205d5dbe8b19d88

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--- Comment #4 from Kenji Hara <k.hara.pg@gmail.com> 2012-02-23 02:38:57 PST ---
I found related bug that returning slice by auto ref causes an error.
----
struct S
{
    int[] a;
    auto ref opSlice(){ return a[]; }  // line 4
}

void main()
{
    S s;
    s[];
}

Output:
----
test.d(4): Error: slice expression this.a[] is not a modifiable lvalue

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |accepts-invalid, pull


--- Comment #5 from Kenji Hara <k.hara.pg@gmail.com> 2012-12-02 22:22:32 PST ---
D2 pull: https://github.com/D-Programming-Language/dmd/pull/1343 https://github.com/D-Programming-Language/phobos/pull/989

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--- Comment #6 from github-bugzilla@puremagic.com 2012-12-06 21:50:15 PST ---
Commits pushed to master at https://github.com/D-Programming-Language/phobos

https://github.com/D-Programming-Language/phobos/commit/7062ce191a651ca94fc779ac646a5ef5653b4559 fix Issue 2486 - taking address of slice rvalue is valid

https://github.com/D-Programming-Language/phobos/commit/af4fea78550216647dbf3e4aaa7d89ab1b79f542 Merge pull request #989 from 9rnsr/fix2486

Issue 2486 - taking address of slice rvalue is valid

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yebblies <yebblies@gmail.com> changed:

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


--- Comment #7 from yebblies <yebblies@gmail.com> 2013-01-07 13:45:08 EST ---
*** Issue 9270 has been marked as a duplicate of this issue. ***

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--- Comment #8 from github-bugzilla@puremagic.com 2013-03-05 22:52:16 PST ---
Commit pushed to master at https://github.com/D-Programming-Language/dmd

https://github.com/D-Programming-Language/dmd/commit/4573ac12bbe1fde782684ed9042f57ab53b05e90 fix Issue 2486 - taking address of slice rvalue is valid

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Andrej Mitrovic <andrej.mitrovich@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |andrej.mitrovich@gmail.com
            Summary|taking address of slice     |taking address of slice
                   |rvalue is valid             |rvalue should not be
                   |                            |allowed


--- Comment #9 from Andrej Mitrovic <andrej.mitrovich@gmail.com> 2013-03-06 05:52:43 PST ---
Changing title to make it easier to understand in changelog.

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