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Why does using std::forward on an rvalue reference cause destruction of the object being referenced?


Why does using std::forward on an rvalue reference cause destruction of the object being referenced?

By : tslpdsgn
Date : November 14 2020, 04:51 PM
Hope this helps It is not destroyed, it is moved from. There is a big difference. Your use of std::forward is also totally incorrect, just FTR.
In this case, std::forward is equivalent to std::move, which means that ptr is moved into the function. A move is like a copy operation but the state of the source object is not preserved. Therefore, unsurprisingly, later, it is empty because it has been moved from.
code :


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How do I forward a rvalue reference?

How do I forward a rvalue reference?


By : Csaba Kiss
Date : March 29 2020, 07:55 AM
With these it helps If value_type is a deduced template parameter, use std::forward(val) (from the header); this is part of the perfect forwarding recipe. If not, and value_type is a specific type (including a non-deduced template parameter), use std::move(val) (also from ). If you take soon's advice and make emplace_back() take a variable number of arguments, that will (most likely) mean using a variadic template and perfect forwarding, which means forward would be the appropriate construct.
Examples:
code :
template<typename... P>
void vector_wrapper::emplace_back( P &&...p ) {
    wrapped_vector_.emplace_back( std::forward<P>(p)... );
}
void vector_wrapper::emplace_back( value_type &&val ) {
    wrapped_vector_.emplace_back( std::move(val) );
}
    // Note: emplace_back() idiomatically uses perfect forwarding,
    // so the first example would typically be more appropriate.
    // This second form is more applicable to push_back()
Are objects inside rvalue referenced object, also rvalue referenced?

Are objects inside rvalue referenced object, also rvalue referenced?


By : Gaurav Sisodiya
Date : March 29 2020, 07:55 AM
Does that help Yes, members of rvalues are themselves rvalues. This was clarified by DR 421
But that is irrelevant here:
Appropriate way to forward rvalue reference

Appropriate way to forward rvalue reference


By : Phan Nguyễn Minh Quâ
Date : March 29 2020, 07:55 AM
should help you out I have the following code: , Citing from Effective Modern C++
code :
void foo(std::string&& str)
{
    bar(str);
}
Why does std::forward converts lvalue and rvalue to rvalue reference?

Why does std::forward converts lvalue and rvalue to rvalue reference?


By : mamadou Diallo
Date : March 29 2020, 07:55 AM
I wish this help you I suppose I am confused with std::forward. My function which uses std::forward is following, but it is much simplified and modified to make explanation easily. ,
why std::forward converts both as rvalue reference
code :
// before reference collapsing
constexpr SomeClass& &&
forward(SomeClass& __t) noexcept
{ return static_cast<SomeClass& &&>(__t); }
// after reference collapsing
constexpr SomeClass&
forward(SomeClass& __t) noexcept
{ return static_cast<SomeClass&>(__t); }
constexpr SomeClass&&
forward(SomeClass& __t) noexcept
{ return static_cast<SomeClass&&>(__t); }
What happen when a lvalue assigned to a rvalue reference? No destruction of the temporary object?

What happen when a lvalue assigned to a rvalue reference? No destruction of the temporary object?


By : Rob
Date : March 29 2020, 07:55 AM
hope this fix your issue Your expectation is wrong. There can't be more destructions than there are constructions.
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