http://d.puremagic.com/issues/show_bug.cgi?id=10625

           Summary: Compiler should warn or disallow using slice syntax in
                    initialization
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Keywords: accepts-invalid
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: andrej.mitrovich@gmail.com


--- Comment #0 from Andrej Mitrovic <andrej.mitrovich@gmail.com> 2013-07-12 09:57:21 PDT ---
-----
void main()
{
    int[] source = [0, 1];

    int[] arr1 = new int[](2);
    arr1[] = source[];

    assert(arr1 !is source);  // ok

    int[] arr2 = source[];  // looks like a copy
    assert(arr2 !is arr2);  // assert fails: but in fact it's not!
}
-----

The 'int[] arr2 = source[];' syntax appears as though the source contents are copied into arr2, but in fact this is the same code as 'int[] arr2 = source;'.

Since [] has a very special meaning, the above should either:

1) Become an actual deep copy, meaning arr2 would have to allocate space first and then copy contents. This would be a breaking and negative change due to performance implications.

2) Not compile. It looks like a deep copy but it isn't, and this can cause issues down the road (for example using memcpy or even OpenGL functions can create hard to track problems due to using the source and target arrays which point to the same memory).

I'd vote heavily towards 2.

Of course one can always use 'int[] arr2 = source.dup'.

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http://d.puremagic.com/issues/show_bug.cgi?id=10625


bearophile_hugs@eml.cc changed:

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--- Comment #1 from bearophile_hugs@eml.cc 2013-07-12 10:33:05 PDT ---
Related to Issue 7445 ?

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