Re: [Boost-users] [lambda] Lambda for member access

18 Apr 2008

      AMDG

Robert Dailey wrote:
...
Hi,
In the Boost.Lambda documentation, it has a section for operators that 
cannot be overloaded, but I'm not really sure if this means you cannot 
use these operators with lambda expressions.
I have the following map:
class SomeClass
{
public:
    void Foo() {}
};
std::map<int, SomeClass> mymap;
I want to be able to do std::for_each() on this map and use lambdas to 
call the Foo() member on each element in the map. For example:
std::for_each( mymap.begin(), mymap.end(), _1.second.Foo() );
Obviously the above does not compile. Is there a way to make this work 
without doing some crazy template specialization? Thanks.
It's pretty ugly:

#include <map>
#include <algorithm>
#include <boost/lambda/lambda.hpp>
#include <boost/lambda/bind.hpp>

class SomeClass
{
public:
    void Foo() {}
};

int main() {

    using boost::lambda::bind;
    using boost::lambda::_1;

    std::map<int, SomeClass> mymap;

    std::for_each( mymap.begin(), mymap.end(),
        bind(&SomeClass::Foo, bind(&std::pair<const int, 
SomeClass>::second, _1)) );
}

You can do the same thing using Boost.Bind, too.

In Christ,
Steven Watanabe