Subject: Re: [boost] Using C++11 lambdas to replace Phoenix in MPL expressions
From: Michel Morin (mimomorin_at_[hidden])
Date: 2012-03-24 23:51:18
Augustus Saunders wrote:
> Lambdas have no default
> constructor, which makes sense, as there would be no way to deal with the capture variables.
> So I'm wondering if anybody can shed some light on manually instantiating lambdas. I would
> think there is a way (possibly shady) to do this, at least for lambdas with no capture.
For lambdas with no capture, the following code might work:
#include <iostream>
int main (int argc, char* argv[])
{
auto x = [](int i){ std::cout << i << std::endl; };
(*static_cast<decltype(x)*>(0))(5);
return 0;
}
But, I strongly discourage its use.
Instead, I recommend wrapping lambdas into boost::optional and
constructing with in-place factories:
#include <boost/optional.hpp>
int main (int argc, char* argv[])
{
auto x = [](int i){ return i * 100; }; // Store type and value in x
boost::optional<decltype(x)> y; // Get type of x and default construct y
y = boost::in_place(x); // Get value of x and lazily construct lambda
return 0;
}
Regards,
Michel