[cfe-dev] [libc++] clang / libc++ fail to compile the code with boost

[Ryuta Suzuki]

Thank you all for your comments and diagnosis.
It sounds like I have to file a bug report to the boost developers.

Cheers,

Ryuta

On Sun, Jul 3, 2011 at 12:29 AM, Howard Hinnant <hhinnant at apple.com> wrote:

> On Jul 2, 2011, at 11:10 AM, Douglas Gregor wrote:
>
> >
> > On Jul 1, 2011, at 7:55 PM, Eli Friedman wrote:
> >
> >> On Fri, Jul 1, 2011 at 7:09 PM, ryuuta <ryuuta at gmail.com> wrote:
> >>> Hi,
> >>> I bet the problem is in boost implementation but
> >>> I'm not 100% sure whether the issue is really on boost side or not.
> <snip>
> >> Testcase without boost:
> >>
> >> #include <map>
> >> struct A { int& x; explicit A(int); public: bool operator<(const A&
> >> other) const {return x < other.x; }};
> >> void f(A* x) { std::map<A, int> y, z; z = y; }
> >>
> >> This looks like a boost bug to me... as far as I can tell, the Key
> >> type of an std::map is required to be assignable if you're assigning
> >> one map to another (although the implementation isn't required to
> >> actually use that assignment operator).
> >
> >
> > C++0x [container.requirements.general] is fairly clear that assigning a
> container requires the element type to be move assignable. This is a Boost
> bug.
>
> Strongly agree.  Especially if you s/copy/move. ;-)  And include the
> reference [associative.reqmts]/p7:
>
> >  The associative containers meet all the requirements of Allocator-aware
> containers (23.2.1), except that for map and multimap, the requirements
> placed on value_type in Table 96 apply instead to key_type and mapped_type.
> [Note: For example, in some cases key_type and mapped_type are required to
> be CopyAssignable even though the associated value_type, pair<const
> key_type, mapped_type>, is not CopyAssignable. —endnote]
>
>
> To be fair to boost, this was at best unspecified in C++03 and no
> implementation of map took advantage of it (erase/insert was/is a common
> algorithm for assignment).  libc++ is probably the first std::lib to recycle
> nodes under associative container assignment.  This can be a huge
> performance win for copy assignment.
>
> Howard
>
>
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