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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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Understanding rvalue references

I think there's something I'm not quite understanding about rvalue references. Why does the following fail to compile (VS2012) with the error 'foo' : cannot convert parameter 1 from 'int' to 'int &&'? void foo(int &&) {} void bar(int &&x) { foo(x);…
moswald
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Preventing non-const lvalues from resolving to rvalue reference instead of const lvalue reference

I'm having trouble overloading a function to take a value either by const reference or, if it is an rvalue, an rvalue reference. The problem is that my non-const lvalues are binding to the rvalue version of the function. I'm doing this in…
Ayjay
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Can std::string overload "substr" for rvalue *this and steal resources?

It just occurred to me I noticed that std::string's substr operation could be much more efficient for rvalues when it could steal the allocated memory from *this. The Standard library of N3225 contains the following member function declaration of…
Johannes Schaub - litb
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Rvalue to lvalue conversion?

Why it is not possible to convert rvalues to lvalues? It is possible to do a conversion in the opposite direction though. Technically rvalues do have a memory address, isn't it?
user8194556
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Why use identity in forward definition for C++0x rvalue reference?

In A Brief Introduction to Rvalue References, forward is defined as follows: template struct identity { typedef T type; }; template T &&forward(typename identity::type &&a) { return a; } What purpose does the…
user2023370
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C++ forwarding reference and r-value reference

I understand that a forwarding reference is "an rvalue reference to a cv-unqualified template parameter", such as in template void foo(T&& ); which means the above function can take both l-value and r-value reference. There's something…
Dave
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Use of rvalue references in function parameter of overloaded function creates too many combinations

Imagine you have a number of overloaded methods that (before C++11) looked like this: class MyClass { public: void f(const MyBigType& a, int id); void f(const MyBigType& a, string name); void f(const MyBigType& a, int b, int c, int d); …
alexc
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Can std::function be move-constructed from rvalue reference to a temporary functor object?

I have an untemplated functor object that I'm trying to store as a std::function inside another object. This object is really heavyweight, so it's marked as uncopyable, but it does have a move constructor. However, trying to construct a…
Crashworks
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Can compiler generate std::move for a last use of lvalue automatically?

A code like this is often seen in r-value references articles: Dave Abrams: Move It With Rvalue References void g(X); void f() { X b; g(b); // still need the value of b … g( std::move(b) ); // all done with b now; grant…
Suma
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Lifetime extension and the conditional operator

local lvalue references-to-const and rvalue references can extend the lifetime of temporaries: const std::string& a = std::string("hello"); std::string&& b = std::string("world"); Does that also work when the initializer is not a simple expression,…
fredoverflow
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What does && mean with a parameter type in C++?

Possible Duplicate: What does T&& mean in C++0x? I had never seen a double ampersand before I read this answer. The code snippet in question is this: template T& as_lvalue(T&& x) { return x; } What does && achieve? What sorts…
paperjam
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Is it possible to obtain the address of the 'this' pointer?

I read that this is an rvalue and we cannot get its address by applying &this. In my code, I have tried to use a reference binding to this. I'm wondering which way will give the address of this? Or are both wrong? What exactly is this? An lvalue, an…
Range Hao
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Why does this rvalue reference bind to an lvalue?

I do not understand why the following code compiles on GCC 8.0: decltype(auto) foo(int&& r) { return r; } In foo, the declaration type of r is int&&, and so the return type of foo is also int&&. But r itself is an lvalue, and an lvalue cannot…
curiousguy12
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C++11 lambda can be assigned to std::function with incorrect signature

The following compiles and runs (under Apple LLVM version 6.1.0 and Visual C++ 2015): #include #include struct s { int x; }; int main(int argc, char **argv) { std::function f = [](const s &p) { std::cout <<…
Eagle
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How to reduce redundant code when adding new c++0x rvalue reference operator overloads

I am adding new operator overloads to take advantage of c++0x rvalue references, and I feel like I'm producing a lot of redundant code. I have a class, tree, that holds a tree of algebraic operations on double values. Here is an example use…
Inverse
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