[boost] Re: functors for taking apart std::pair?

[Marshall Clow]

At 7:21 AM -0400 7/10/03, David Abrahams wrote:
Marshall Clow <[EMAIL PROTECTED]> writes:

 > So, here they are. Are they useful to anyone else? Is there some 
reason that
 they don't already exist? Did I miss them somewhere?

 template <class T1, class T2>
 struct first: std::unary_function< std::pair <T1, T2>, T1>
 {
        T1 operator()(const std::pair <T1, T2> & x) const { return x.first;}
 };
 template <class T1, class T2>
 struct first: std::unary_function< std::pair <T1, T2>, T2>
 {
        T2 operator()(const std::pair <T1, T2> & x) const { return x.second;}
 };
The second one appears to be misnamed.
Yeah. :-(
Teach me to try to "boostify" them using an email client.
But other than that, what do people think?

I needed them because someone had a map<int, Foo*>, and I wanted to 
call a member function
(call it "Bar") on each Foo* in the map. Turns out, that with 
boost::compose and 'second', it
was simple:

	std::for_each ( m.begin (), m.end (),
		boost::compose_f_gx ( std::mem_fun ( Foo::Bar ), 
second <int, Foo *> ()));

--
-- Marshall
Marshall Clow     Idio Software   <mailto:[EMAIL PROTECTED]>
Hey! Who messed with my anti-paranoia shot?
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