Question

Needless to over explain. The following code is self-evident:

struct X
{
    X(int n){}
};

int main()
{
    std::vector<int> src;
    std::vector<X>   dest;

    // Below is not valid in current C++, but that is just what I want.
    transform(src.begin(), src.end(), back_insert(dest), std::bind(&X::X, _1)); 
}

A constructor takes some arguments and returns an object of the class of the constructor.

A constructor looks like a function, acts like a function, and is exactly a function.

So, I think std::bind should uniformly treat constructors and other callable objects.

However, how can I extend the function template “bind” to implement that?

Answer 1

Since X is implicitly constructible from int, a simple copy should achieve the conversion.

copy(src.begin(), src.end(), std::back_inserter(dest)); 

Or even using the vector’s constructor:

std::vector<X>   dest(src.begin(), src.end());

In the general case, boost’s lambda library has a constructor functor.

#include <boost/lambda/bind.hpp>
#include <boost/lambda/construct.hpp>
...
using namespace boost::lambda;
transform(src.begin(), src.end(), std::back_inserter(dest), bind(constructor<X>(), _1));

In this particular case binding might not be necessary, since there is only one argument to constructor.