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

From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2008-04-17 20:14:00

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