Unnecessary copies

[sean-parent]

The following code creates an unnecessary copy (internally it is because get_try() is returning an optional instead of an optional<const T&>). It also does 4 moves. Can that be reduced?

#include <iostream>

#include <stlab/concurrency/future.hpp>
#include <stlab/concurrency/immediate_executor.hpp>

using namespace stlab;
using namespace std;

struct annotate {
    annotate() { cout << "annotate ctor" << endl; }
    annotate(const annotate&) { cout << "annotate copy-ctor" << endl; }
    annotate(annotate&&) noexcept { cout << "annotate move-ctor" << endl; }
    annotate& operator=(const annotate&) {
        cout << "annotate assign" << endl;
        return *this;
    }
    annotate& operator=(annotate&&) noexcept {
        cout << "annotate move-assign" << endl;
        return *this;
    }
    ~annotate() { cout << "annotate dtor" << endl; }
    friend inline void swap(annotate&, annotate&) { cout << "annotate swap" << endl; }
    friend inline bool operator==(const annotate&, const annotate&) { return true; }
    friend inline bool operator!=(const annotate&, const annotate&) { return false; }
};

template <class T>
inline auto promise_future() {
    return package<T(T)>(immediate_executor, [](auto&& x) -> decltype(x) { return std::forward<decltype(x)>(x); });
}

int main() {
    auto [promise, future] = promise_future<annotate>();
    promise(annotate());
    future.then([](const annotate&){ }); // copy happens here!
}

[sean-parent]

I just started the branch copy-less to resolve this issue. It addresses this particular copy but still there are a fairly large number of other cases to handle. I published the branch for reference and will try and make time to complete it.

[FelixPetriconi]

Use copy_less branch, but leave the issue open

[fosterbrereton]

This issue has been fixed in master as of the 1.1 release.