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When the class object that a function returns is a function parameter, copy elision is not possible. T.C:8:20: note: remove ‘std::move’ call -Wredundant-move T.C:8:20: warning: moving a local object in a return statement prevents copy elision So GCC 9 will issue a warning (when -Wall is in effect): The reason for this is that std::move returns a reference, and in general, the compiler can't know to what object the function returns a reference to. However, here the call to std::move precludes the NRVO, because it breaks the conditions specified in the C++ standard, namely : the returned expression must be a name.
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Word developer tools move anywhere code#
Some programmers might be tempted to "optimize" the code by putting std::move into the return statement like this: In this case, this optimization is simply Return Value Optimization (RVO). For example, the return statement in the function fn above might be return T() and copy elision would still apply. The object a function returns doesn't need to have a name. (Note that this optimization does not depend on any of the -O levels.) For instance: This is what we call Named Return Value Optimization (NRVO).
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Additionally, C++17 says that copy elision is mandatory in certain situations.
Word developer tools move anywhere free#
The compiler is free to perform this optimization even when the move/copy construction has side effects. In such a case, the compiler can construct the object directly in its final destination (i.e., in the caller's stack frame). When returning a local variable of the same class type as the function return type, the compiler is free to omit any copying or moving (i.e., perform copy/move elision), if the variable we are returning is a non-volatile automatic object and is not a function parameter. In this article, I will introduce two new warnings I've implemented for GCC 9 that deal with incorrect usage of std::move. Fortunately, the compiler can sometimes help with finding such wrong uses of std::move. However, std::move must be used judiciously using it blithely may lead to performance degradation, or simply be redundant, affecting readability of the code. This version of swap consists of one move construction and two move assignments and does not involve any deep copies. All is well. For example, we can write a more effective version of swap using std::move: std::move merely casts its argument to an rvalue reference to allow moving it, but doesn't guarantee a move operation. The standard C++ library gained a function template called std::move, which, despite its name, does not move anything. Move semantics came along with several more or less related features, such as rvalue references, xvalues, forwarding references, perfect forwarding, and so on. Essentially, you can think of it as turning a deep copy into a shallow copy. Move semantics is a way to avoid expensive deep copy operations and replace them with cheaper move operations.
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One of the most important concepts introduced in C++11 was move semantics.