allowed to perform URVO since C++98 • Compilers are required to provide URVO support since C++17 • NRVO support is optional, but recommended TechAtBloomberg.com © 2024 Bloomberg Finance L.P. All rights forces G++ to call the copy constructor in all cases. MSVC disables NRVO by default XxxleXXoXXstXX ... can be enabled using /Zc:nrvo, which is turned on automatically with the /O2 optimization, the /permissive- #include using namespace std; g++ -std=c++17 -O0 -fno-elide-constructors nrvo.cpp -o nrvoOFF g++ -std=c++17 -O0 nrvo.cpp -o nrvoON class MyObj { public: int a; int* b; MyObj(int x) {

var T from p specifies a type varTy $$ T, 2 $$ which is incompatible with varTy $$ T, 1 $$ . ## NRVO Note: This section describes the current implementation. This part of the language specification variable. This allows for a mechanism much like C++'s "named return value optimization" (NRVO). NRVO means that the stores to result inside p directly affect the destination dest in let/var dest = return type. NRVO applies for T if $ \text{sizeof}(T) >= N $ (where N is implementation dependent), in other words, it applies for "big" structures. If p can raise an exception, NRVO applies regardless

Symmetry C++ Techniques to cheat object lifecycle symmetry: • (Named-)Return Value Optimization (RVO, NRVO) to transfer instance • “Pilfer” or transfer object state: • xvalues ( $ &\& $ ) (since binary operator overloads (left- operand is always *this) (Named-)Return Value Optimization (RVO, NRVO) to transfer instance xvalues ( $ &\& $ ) (since C++11) to pilfer or transfer instance state state") • Temporary objects (i.e., prvalue “materialization”) • xvalues (“eXpiring values”) • RVO, NRVO (Named-Return Value Optimization) ## Hierarchy Hygiene C++ inheritance exhibits ___ outstanding symmetry

compiler can optimize the code and avoid temporary copies. This is a well-known optimization, called NRVO (Named Return Value Opti- mization), in languages like C $ ^{++} $ . $ ^{[3]} $ Programmers often

compiler can optimize the code and avoid temporary copies. This is a well-known optimization, called NRVO (Named Return Value Optimization), in languages like C++. $ ^{[3]} $ Programmers often prefer to

compiler can optimize the code and avoid temporary copies. This is a well-known optimization, called NRVO (Named Return Value Opti- mization), in languages like C $ ^{++} $ . $ ^{[3]} $ Programmers often

compiler can optimize the code and avoid temporary copies. This is a well-known optimization, called NRVO (Named Return Value Opti- mization), in languages like C $ ^{++} $ . $ ^{[3]} $ Programmers often

compiler can optimize the code and avoid temporary copies. This is a well-known optimization, called NRVO (Named Return Value Optimization), in languages like C++. $ ^{[3]} $ Programmers often prefer to

compiler can optimize the code and avoid temporary copies. This is a well-known optimization, called NRVO (Named Return Value Optimization), in languages like C++. $ ^{[3]} $ Programmers often prefer to

compiler can optimize the code and avoid temporary copies. This is a well-known optimization, called NRVO (Named Return Value Optimization), in languages like C++. $ ^{[3]} $ Programmers often prefer to