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Questions tagged [rvalue-reference]

An rvalue reference is a new language feature in C++11 representing a reference to an rvalue. Together with reference collapsing, they are used to implement and enable move semantics and perfect forwarding.

An rvalue reference is a language feature added in C++11 (formerly known as C++0x). It is used to bind to an rvalue thus extending the temporary object's lifetime.

Together with reference collapsing, they are used to implement and enable move semantics and perfect forwarding.

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function && qualifier behaviour

I'm confused by the following code: struct test { void f() & { std::cout << "&" << std::endl; } void f() const& { std::cout << "const&" << std::endl; } void f() && { std::cout << "&&" << std::endl; } void f() const&& { …
Tim
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Can an rvalue reference bind to a function?

I tested the following code with GCC, Clang, ICC and VS: void f() {} void g(void (&&)()) { } int main() { g(f); } As we can see, g takes an rvalue reference but f is an lvalue and, in general, rvalue references cannot be bound to lvalues.…
Cassio Neri
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Assigning this pointer to rvalue reference to a pointer

Should the following sample compile? struct B; struct A { A(B*&&){} }; struct B : A { B() : A(this){} }; int main(){} On LWS with clang it compiles, but with gcc I get: no known conversion for argument 1 from 'B* const' to 'B*&&' and if I…
Jesse Good
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Move Semantics and Pass-by-Rvalue-Reference in Overloaded Arithmetic

I am coding a small numeric analysis library in C++. I have been trying to implement using the latest C++11 features including move semantics. I understand the discussion and top answer at the following post: C++11 rvalues and move semantics…
Tientuinë
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Move semantics - what it's all about?

Possible Duplicate: Can someone please explain move semantics to me? Could someone point me to a good source or explain it here what are the move semantics?
smallB
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Conditional compilation for move operations

How can I check whether my compiler supports rvalue references or not? Is there a standard preprocessor macro, or do different compilers have different macros? Ideally, I would want to write this: #ifdef RVALUE_REFERENCES_SUPPORTED foobar(foobar&&…
fredoverflow
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Is it possible to return the current object if it is an r-value reference?

I have recently learned about r-value references. In order to more thoroughly experiment I decided to write a simple DenseMatrix class. My question is is it possible to write any function ( Transpose for this example ) such that for auto A =…
Hen3
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rvalue for a std::string parameter

What's the difference in practice between LVALUE and RVALUE in the following code when I pass the text? I mean, in this specific case of a string (where the string is a string literal), is there any benefit of using RVALUE (&&)? void…
anc
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What is multimap::emplace() and move()?

I was viewing the MSDN doc about multimap and find that it has a member function multimap::emplace(). Below is the example of that member function. int main( ) { using namespace std; multimap m1; pair is1(1,…
MorrisLiang
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Is it necessary to define move constructors from different classes?

Consider the following: struct X { Y y_; X(const Y & y) :y_(y) {} X(Y && y) :y_(std::move(y)) {} }; Is it necessary to define a constructor like the second one in order to take full advantage of move semantics? Or will it be taken…
Benjamin Lindley
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Why is T&& instantiated as int&?

Can anyone please explain why this compiles and why does t end up with type int&? #include void f(int& r) { ++r; } template void g(Fun fun, T&& t) { fun(std::forward(t)); } int main() { int i…
Šimon Tóth
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Can't bind lvalue to rvalue reference

I have this C++ test code snippet, #include class A { std::vector x; public: A(std::vector&& _x) : x(_x) {} }; class B { A a; public: B(std::vector&& _x) : a(/*move(*/_x/*)*/) {} }; I'm…
Samik
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Can an rvalue be moved into a shared_ptr

Is it possible to 'move' an rvalue into a shared_ptr. All the methods which I've tried so far result in a copy. My desired usage pattern is: class Element { public: Element(const string &); Element(const Element &) = delete; //delete copy…
Elliot Woods
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Variables declared by &&

Thinking about (x|r|l|pr|gl)values, the following question came to my mind: Consider the following two variable declarations: X x = ...; and X&& x = ...; and assume the ... do not deliver an xvalue. Can anybody think of code not using decltype in…
JohnB
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Move from *this in an rvalue method?

In C++11, methods can be overloaded on whether or not the expression that denotes the object on which the method is called is an lvalue or an rvalue. If I return *this from a method called via an rvalue, do I need to explicitly move from *this or…
fredoverflow
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