How Can I Achieve Move Capture in C 11 Lambdas?

Capturing by Move in a C 11 Lambda

Move Capture in C 14

C 14 introduces generalized lambda capture, which allows for move capture. This feature enables code like:

using namespace std;

auto u = make_unique<some_type>(some, parameters);  

go.run([u = move(u)] { do_something_with(u); }); 

Workaround for Move Capture in C 11

In C 11, move capture can be emulated using a helper function make_rref:

#include <cassert>
#include <memory>
#include <utility>

template <typename T>
struct rref_impl
{
    // ... (implementation omitted for brevity)
};

template<typename T> rref_impl<T> make_rref( T && x )
{
    return rref_impl<T>{ std::move(x) };
}

Example usage:

std::unique_ptr<int> p{new int(0)};
auto rref = make_rref(std::move(p));
auto lambda = [rref]() mutable -> std::unique_ptr<int> { return rref.move(); };
assert(lambda());
assert(!lambda());

Emulating Generalized Lambda Capture in C 11

Generalized lambda capture can also be emulated using a capture function:

#include <utility>

template <typename T, typename F>
class capture_impl
{
    // ... (implementation omitted for brevity)
};

template <typename T, typename F>
capture_impl<T,F> capture( T && x, F && f )
{
    // ... (implementation omitted for brevity)
}

Example usage:

std::unique_ptr<int> p{new int(0)};
auto lambda = capture(std::move(p), [](std::unique_ptr<int> &p) { return std::move(p); });
assert(lambda());
assert(!lambda());

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