Boost C++ Libraries: Ticket #3395: Assignment to optional is not possible if operator& is overriden

Andrey Semashev — Thu, 03 Sep 2009 07:02:43 GMT

BTW, I just now noticed that the assignment operator accepts its argument by value. It may be worth to accept it by const reference, as the operator is not only called for in-place factories but also for other types. For example:

struct MyString
{
    MyString(std::string const&);
};
std::string str = "Hello";
boost::optional< MyString > opt;
opt = str; // here a needless copy of str will be constructed

I'm attaching an updated patch that fixes this, too.

attachment set

Andrey Semashev — Thu, 03 Sep 2009 07:04:03 GMT

attachment → optional.hpp.patch

An updated fix that also optimises away copying the assignment argument

Andrey Semashev — Sun, 05 Dec 2010 14:43:21 GMT

(In [67020]) Refs #3395. Optional construction and assignment now works correctly for types with overridden operator&. Also silenced some GCC warnings about broken strict aliasing rules.

attachment set

Ralf W. Grosse-Kunstleve — Wed, 08 Dec 2010 02:57:48 GMT

attachment → zd

proposed patch for review

Ralf W. Grosse-Kunstleve — Wed, 08 Dec 2010 03:01:47 GMT

The current optional.hpp leads to gcc 3.2 warnings (Redhat 8.0). It is easily fixed with the proposed patch I attached a minute ago. Is this OK to commit? -- It is tested already locally on a large number of platforms.

Steven Watanabe — Wed, 08 Dec 2010 16:52:42 GMT

Replying to rwgk:

The current optional.hpp leads to gcc 3.2 warnings (Redhat 8.0). It is easily fixed with the proposed patch I attached a minute ago. Is this OK to commit? -- It is tested already locally on a large number of platforms.

This looks good to me.

anonymous — Wed, 08 Dec 2010 17:16:52 GMT

Looks good to me as well. Please go ahead and commit.

Andrey Semashev — Wed, 08 Dec 2010 17:50:07 GMT

Perhaps, the patch should also take into account GCC versions prior to 3.2? I really don't know since which version may_alias has become available.

Ralf W. Grosse-Kunstleve — Wed, 08 Dec 2010 18:01:25 GMT

I checked in my patch as svn trunk rev. [67109] before seeing comment 6.

Is anyone still using a gcc before 3.2? Even 3.2 is ancient now (released 2002). It is the oldest gcc I have, i.e. I couldn't test with any older versions.

Andrey Semashev — Wed, 08 Dec 2010 18:52:18 GMT

That's ok, I've updated your change with a check for earlier GCC versions. Try with the updated version.

anonymous — Thu, 09 Dec 2010 16:23:01 GMT

It ran without a problem in our nightly builds (24 platforms). Thanks!

status changed; resolution set

Andrey Semashev — Sun, 12 Dec 2010 11:34:16 GMT

status new → closed
resolution → fixed

(In [67183]) Merged changes from trunk. Fixes #3395. Also updates swap behavior: if default constructor has no-throw guarantee, swap will use it to provide no-throw guarantee itself. operator>> behavior changed slightly so that the stream is not accessed when unrecognized character sequence is detected. The stream is marked with failbit in such a case.