Extracting pair member in lambda expressions and template typedef idiom
- by Nazgob
Hi, I have some complex types here so I decided to use nifty trick to have typedef on templated types. Then I have a class some_container that has a container as a member. Container is a vector of pairs composed of element and vector. I want to write std::find_if algorithm with lambda expression to find element that have certain value. To get the value I have to call first on pair and then get value from element. Below my std::find_if there is normal loop that does the trick. My lambda fails to compile. How to access value inside element which is inside pair?
I use g++ 4.4+ and VS 2010 and I want to stick to boost lambda for now.
#include <vector>
#include <algorithm>
#include <boost\lambda\lambda.hpp>
#include <boost\lambda\bind.hpp>
template<typename T>
class element
{
public:
T value;
};
template<typename T>
class element_vector_pair // idiom to have templated typedef
{
public:
typedef std::pair<element<T>, std::vector<T> > type;
};
template<typename T>
class vector_containter // idiom to have templated typedef
{
public:
typedef std::vector<typename element_vector_pair<T>::type > type;
};
template<typename T>
bool operator==(const typename element_vector_pair<T>::type & lhs, const typename element_vector_pair<T>::type & rhs)
{
return lhs.first.value == rhs.first.value;
}
template<typename T>
class some_container
{
public:
element<T> get_element(const T& value) const
{
std::find_if(container.begin(), container.end(), bind(&typename vector_containter<T>::type::value_type::first::value, boost::lambda::_1) == value);
/*for(size_t i = 0; i < container.size(); ++i)
{
if(container.at(i).first.value == value)
{
return container.at(i);
}
}*/
return element<T>(); //whatever
}
protected:
typename vector_containter<T>::type container;
};
int main()
{
some_container<int> s;
s.get_element(5);
return 0;
}
