Re: [Boost-users] [boost][lexical_cast] simple example doesn't work with vector<T>

From: Ovanes Markarian (om_boost_at_[hidden])
Date: 2008-04-07 17:43:22

Yes, that's true...

the std operator << is defined as:

template<class CharT, class Traits>
basic_ostream<CharT, Traits>& operator<<(basic_ostream<CharT, Traits>,
some_overloaded_type const&);

due some_overaloaded_type is not a template argument, the template can not
be specialized on it, and therefore it is illegal to overload this operator.

Andy, to your other post:

standard only says that this is undefined behavior to overload std functions
if it works with your compiler it does not mean it will always work and that
it will not break existing code or cause some sleepless night to another
developer why some other operator << then the std one is called.

This is just a reminder, that not everything that compiles is automatically
standard conform.

Best Regards,
Ovanes

On 4/7/08, Steven Watanabe <watanabesj_at_[hidden]> wrote:
>
> AMDG
>
>
> Ovanes Markarian wrote:
> > Just an addition:
> >
> > Explicit specialization of std templates is legal. So if you _exactly_
> > know vector types for which your <<-operator should work you can write:
> >
> > namespace std
> > {
> >   template<>
> >   ostream& operator<< (ostream& os, const vector<MyTypeX>& v)
> >   {
> >     copy(v.begin(), v.end(), ostream_iterator<T>(os, ";"));
> >     return os;
> >   }
> > }
> >
> > By the way there was a big discussion about this on std list and I
> > fluently read the upcoming Standard draft and saw that this paragraph
> > changed. I not any longer sure if this will be allowed with the new
> > standard.
>
>
> There has to be template to specialize.  The std library doesn't have
> an overload of operator<< that matches std vector.  Specialization
> can't change that.
>
>
> In Christ,
> Steven Watanabe
>
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