[Bug libstdc++/65714] New: shared_ptr<void>::reset(p) blows a static_assertion

[Bug libstdc++/65714] New: shared_ptr<void>::reset(p) blows a static_assertion

[john.salmon at deshaw dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65714

            Bug ID: 65714
           Summary: shared_ptr<void>::reset(p) blows a static_assertion
           Product: gcc
           Version: 4.9.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: john.salmon at deshaw dot com

The single-argument form of shared_ptr::reset fails with a static assertion
when the pointer type is void.

drdws0047$ cat spv.cpp
#include <memory>
#include <cstdlib>

void foo(){
    std::shared_ptr<void> spv( ::malloc(1024), ::free );
    spv.reset(::malloc(2048));     // .../shared_ptr_base.h:874:4: error:
static assertion failed: incomplete type
    spv.reset(::malloc(2048), ::free);  // looks ok.
}




drdws0047$ dw -m gcc/4.9.2-30B/bin g++ -std=c++14 spv.cpp
In file included from
/proj/desrad-c/root/Linux/x86_64/gcc/4.9.2-30B/include/c++/4.9.2/bits/shared_ptr.h:52:0,
                 from
/proj/desrad-c/root/Linux/x86_64/gcc/4.9.2-30B/include/c++/4.9.2/memory:82,
                 from spv.cpp:1:
/proj/desrad-c/root/Linux/x86_64/gcc/4.9.2-30B/include/c++/4.9.2/bits/shared_ptr_base.h:
In instantiation of ‘std::__shared_ptr<_Tp, _Lp>::__shared_ptr(_Tp1*) [with
_Tp1 = void; _Tp = void; __gnu_cxx::_Lock_policy _Lp =
(__gnu_cxx::_Lock_policy)2u]’:
/proj/desrad-c/root/Linux/x86_64/gcc/4.9.2-30B/include/c++/4.9.2/bits/shared_ptr_base.h:1023:4:
  required from ‘void std::__shared_ptr<_Tp, _Lp>::reset(_Tp1*) [with _Tp1 =
void; _Tp = void; __gnu_cxx::_Lock_policy _Lp = (__gnu_cxx::_Lock_policy)2u]’
spv.cpp:6:29:   required from here
/proj/desrad-c/root/Linux/x86_64/gcc/4.9.2-30B/include/c++/4.9.2/bits/shared_ptr_base.h:874:4:
error: static assertion failed: incomplete type
    static_assert( !is_void<_Tp1>::value, "incomplete type" );
    ^
drdws0047$
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id1247

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |WONTFIX

--- Comment #17 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Noone is convinced this would be a positive change, let's close it.

[Bug libstdc++/65714] shared_ptr<void>::reset(p) blows a static_assertion

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65714

Jonathan Wakely <redi at gcc dot gnu.org> changed:

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

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
The standard says s.reset(p) is equivalent to shared_ptr(p).swap(s) and
shared_ptr(p) requires that p is a pointer to a complete type.

A void* is not a pointer to a complete type.

If your code compiled it would end up calling 'delete' on a void*, which is
invalid, and would not be suitable for memory allocated by malloc() anyway.