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digitalmars.D.bugs - [Issue 8901] New: a bug to cast from array literal to ubyte[]

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8901

           Summary: a bug to cast from array literal to ubyte[]
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: enjouzensyou.boinc gmail.com



06:22:19 PDT ---
import std.stdio;

void main()
{
    int a = 12321;
    int[] arr = [a];

    assert( (cast(ubyte[])[a])
                == (cast(ubyte[])arr) );
}


This code doesn't work!

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next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8901


hsteoh quickfur.ath.cx changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hsteoh quickfur.ath.cx



I don't understand, why should this work?

D arrays are not the same as C arrays; casting an int into an array does not
magically make it an array of bytes.

If you want to get the byte representation, you need to do something like this:

int a = 1234;
ubyte* ptr = cast(ubyte*)&a;
writeln(ptr[0 .. int.sizeof]);

Note, though, that this is unsafe, and is generally not recommended in D code,
unless you're writing low-level code.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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hsteoh quickfur.ath.cx changed:

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


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prev sibling next sibling parent d-bugmail puremagic.com writes:
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Haha, case in point: that slice operation should be ptr[0 .. int.sizeof-1].

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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Oh wait, no, the original was correct. :-/  See what I mean? It's unsafe. :)

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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SHOO <zan77137 nifty.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
                 CC|                            |zan77137 nifty.com
         Resolution|INVALID                     |



This is like the bug somehow or other. However, by the document of the Web, it
does not seem to be touched about the explicit cast from array to array deeply.
In the current implementation, it is worked by _d_arraycast in druntime. The
cast is performed safely, and it throws Error if misalignment occurs.

This bug seems to happen, because `cast(ubyte[])[a]` is processed as
`cast(ubyte[])[cast(ubyte)a]` by dmd.
`[a]` should be always processed as `int[]`.

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Oct 28 2012
prev sibling parent d-bugmail puremagic.com writes:
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yebblies <yebblies gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|REOPENED                    |RESOLVED
                 CC|                            |yebblies gmail.com
         Resolution|                            |INVALID





 
 This bug seems to happen, because `cast(ubyte[])[a]` is processed as
 `cast(ubyte[])[cast(ubyte)a]` by dmd.
 `[a]` should be always processed as `int[]`.


That is not a bug, casting an array literal is not the same as casting an
array/slice.  While this is an inconsistent design, it is definitely
intentional.

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