CODEWITHSUNDEEP
c++g++c++17clang++
osovan
osovan

Reputation: 47

Compilation error declaring a unique_ptr member in a class

It is some kind of factory lambda. The class to be instantiated by the lambda receives a reference to another class in its constructor. If the latter declares a unique_ptr member, a really long error is thrown:

#include <memory>
#include <string>

struct A
{
    std::unique_ptr<int> foo;
};

struct B
{
    B(const std::string & str, A&a) {}
};

template<typename T, typename ... Args>
auto registerType(const std::string & type, Args&& ... args)
{

    return [args = std::make_tuple(std::forward<Args>(args) ...)]() mutable -> auto
    {
        return std::apply([](auto&& ... args){
            return std::make_unique<T>(args ...);
        }, std::move(args));
    };
}

int main()
{
    A a;
    registerType<B>("lala", "p1", a)();
}

Removing the unique_ptr member works fine. Passing a pointer to 'a' instead of a reference also works fine.

Error output is long, better to see it in action:

https://godbolt.org/z/n896qMz59

This happens at least with:

Any ideas?

Thanks

Upvotes: 1

Views: 167

Answers (1)

Ted Lyngmo
Ted Lyngmo

Reputation: 117298

You can't copy a unique_ptr.

But you can move it:

#include <utility>

// ...

registerType<B>("lala", "p1", std::move(a))();

or prevent the std::decay when using make_tuple from happening:

return [args = std::tuple<Args...>(std::forward<Args>(args) ...)]() mutable -> auto

Upvotes: 3

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