http://d.puremagic.com/issues/show_bug.cgi?id=9904

           Summary: typeof(null) can be casted to aggregate type if
                    .sizeof equals size of pointer
           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> 2013-04-08 07:42:22 PDT ---
struct S1
{
    int x;
}

struct S2
{
    int x;
    byte b;
}

void main()
{
    static assert(S1.sizeof == typeof(null).sizeof);
    auto s1 = cast(S1)null;  // compiles, should not

    static assert(S2.sizeof != typeof(null).sizeof);
    auto s2 = cast(S2)null;  // NG, as it should
}

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--- Comment #1 from Andrej Mitrovic <andrej.mitrovich@gmail.com> 2013-04-08 07:47:34 PDT ---
(In reply to comment #0)
> struct S1
> {
>     int x;
> }
> 
> struct S2
> {
>     int x;
>     byte b;
> }

Those should really use size_t to reproduce on all systems:

> struct S1
> {
>     size_t x;
> }
> 
> struct S2
> {
>     size_t x;
>     byte b;
> }

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bearophile_hugs@eml.cc changed:

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


--- Comment #2 from bearophile_hugs@eml.cc 2013-04-08 10:01:36 PDT ---
(In reply to comment #1)

> Those should really use size_t to reproduce on all systems:
> 
> > struct S1
> > {
> >     size_t x;
> > }
> > 
> > struct S2
> > {
> >     size_t x;
> >     byte b;
> > }

Why is that cast a problem/bug? Maybe there is no compiler bug here.

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--- Comment #3 from Andrej Mitrovic <andrej.mitrovich@gmail.com> 2013-04-08 10:31:56 PDT ---
(In reply to comment #2)
> (In reply to comment #1)
> 
> > Those should really use size_t to reproduce on all systems:
> > 
> > > struct S1
> > > {
> > >     size_t x;
> > > }
> > > 
> > > struct S2
> > > {
> > >     size_t x;
> > >     byte b;
> > > }
> 
> Why is that cast a problem/bug? Maybe there is no compiler bug here.

It may not do what the user expects. For example they might think this is a good way to initialize the struct to its default value, but it's wrong:

import std.math;

struct S
{
    float x;
}

void main()
{
    auto s1 = S.init;
    auto s2 = cast(S)null;
    assert(isnan(s1.x));
    assert(isnan(s2.x));  // fails
}

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--- Comment #4 from github-bugzilla@puremagic.com 2013-06-07 22:19:54 PDT ---
Commits pushed to master at https://github.com/D-Programming-Language/dmd

https://github.com/D-Programming-Language/dmd/commit/d859a617045bdf04b39edf14bb782faff642141a
fix issue 9904 - typeof(null) can be casted to aggregate type if .sizeof
equals size of pointer

https://github.com/D-Programming-Language/dmd/commit/3c5eb896fb87b788dd0cb7631fbdf8c5cf77d9f2 Merge pull request #2148 from hpohl/9904

fix issue 9904 - typeof(null) can be casted to aggregate type if .sizeof equals
size of pointer

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

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


--- Comment #5 from Kenji Hara <k.hara.pg@gmail.com> 2013-06-07 22:20:34 PDT ---
Merged pull request: https://github.com/D-Programming-Language/dmd/pull/2148

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