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Re: Second GCC 4.7.0 Release Candidate available from gcc.gnu.org


Hi,

On 03/19/2012 01:38 PM, Jonathan Wakely wrote:
2012/3/19 Jonathan Wakely<jwakely.gcc@gmail.com>:
2012/3/19 PaweÅ Sikora:
On Wednesday 14 of March 2012 12:22:41 Richard Guenther wrote:
GCC 4.7.0 Release Candidate available from gcc.gnu.org

A second release candidate for GCC 4.7.0 is available from

ftp://gcc.gnu.org/pub/gcc/snapshots/4.7.0-RC-20120314

and shortly its mirrors. It has been generated from SVN revision 185376.

I have so far bootstrapped and tested the release candidate on
x86_64-linux.  Please test it and report any issues to bugzilla.
i'd like to ask about simple code snipet rejected by 4.7.0-RC2:

#include<boost/shared_ptr.hpp>
#include<map>
#include<string>

typedef boost::shared_ptr<std::string>  HString;
typedef std::map<std::string,HString>  StrAttribsT;
StrAttribsT m_str_attribs;

void foo(const char* attribName, const char* value)
{
        m_str_attribs.insert(std::make_pair(attribName, new std::string(value)));
}

it compiles cleanly with 'g++46 -std=gnu++0x' but 4.7 rejects this code.
is it an effect of 'name lookup changes'? (http://gcc.gnu.org/gcc-4.7/porting_to.html)
No, the change is in how std::pair is constructed, the code can be reduced to:

#include<boost/shared_ptr.hpp>
#include<string>

typedef boost::shared_ptr<std::string> HString;

void foo(const char* attribName)
{
    const std::pair<const std::string, HString>  a
        = std::make_pair(attribName, new std::string);
}

Probably caused by http://gcc.gnu.org/viewcvs?view=revision&revision=174464

I haven't looked in enough detail to see if the change in behaviour is
correct or a regression.
My guess is that the new behaviour is correct, because the relevant
constructor of boost::shared_ptr is 'explicit' but you're relying on
an implicit conversion from pair<const char*, string*>  to
pair<std::string, shared_ptr<string>>  which implicitly converts a raw
pointer to a shared_ptr.
Probably, yes. We should double check your analysis (thanks!)

In 4.7 we indeed have much more constraining in std::pair, but first blush it's correct, per C++11 I mean (there is also the DR about using is_constructible instead of is_convertible in std::map, still unimplemented, but I don't think it's related and goes beyond C++11 anyway)

Paolo.


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