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digitalmars.D.bugs - [Issue 10512] New: Reinterpret-casting struct fields as another struct should be safe

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=10512

           Summary: Reinterpret-casting struct fields as another struct
                    should be  safe
           Product: D
           Version: unspecified
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: tommitissari hotmail.com


--- Comment #0 from Tommi <tommitissari hotmail.com> 2013-06-30 11:08:15 PDT ---
The order and alignment of struct fields are statically known. Therefore the
compiler should be able to verify that the following code is memory safe and
let it compile:

 safe:

struct A
{
    int   i;
    short s;
    byte  b;
}

struct B
{
    long  l;
    int   i;
    short s;
    byte  b;
}

void main()
{
    A a;
    B b;
    *(cast(A*) &b.i) = a; // [1]
}

[1] Error: cast from int* to A* not allowed in safe code

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parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=10512


Maxim Fomin <maxim maxim-fomin.ru> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |maxim maxim-fomin.ru


--- Comment #1 from Maxim Fomin <maxim maxim-fomin.ru> 2013-06-30 11:40:49 PDT
---
These structs may come from different implementations with different
alignments. In general case structs may include other aggregate types where
situation may be complicated. D has unions for such tricks (you are better with
placing long l in last place). In my opinion this is wontfix.

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