Re: [Boost-users] Defining less on member variables/functions

26 Mar 2004


      --- At Fri, 26 Mar 2004 00:48:49 +0100, Daniel Wallin wrote:
...
Chris Jurney wrote:
...
I've had this same pattern come up 4 or 5 times now, and each time I've 
been unable to find a stl + boost solution that allowed me to do what I 
want without writing my own less function.  Basically, I want something 
that will let me do a sort, or define a map on structs or pairs without 
writing a less that compares the member variable or .first.  
<snip>
No such luck.  It looks like I can do operator * and & on lambda 
objects, but not access members through them.  Is there anything in 
boost, stl, or elsewhere that lets me not write this:
class myLess
{
bool operator() (pair a, pairb)
{return a.first < b.first;}
}
Yes:
struct X
  {
      int a;
  };
std::vector<X> v;
With boost.bind:
std::sort(
      v.begin()
    , v.end()
    , boost::bind(
          std::less<int>()
        , boost::bind(&X::a, _1)
        , boost::bind(&X::a, _2)
      )
  );
I don't know lambda, so I won't comment on that. But, I thought that the
first parameter to bind was a function pointer? You can bind to an address? 

Please explain how this works?
...
and with boost.lambda:
std::sort(
        v.begin()
      , v.end()
      , bind(&X::a, _1) < bind(&X::a, _2)
    );
...Duane

Re: [Boost-users] Defining less on member variables/functions

Duane Murphy