perfect-forwarding

Perfect Forwarding to async lambda

Deadly 提交于 2020-12-02 06:49:20
问题 I have a function template, where I want to do perfect forwarding into a lambda that I run on another thread. Here is a minimal test case which you can directly compile: #include <thread> #include <future> #include <utility> #include <iostream> #include <vector> /** * Function template that does perfect forwarding to a lambda inside an * async call (or at least tries to). I want both instantiations of the * function to work (one for lvalue references T&, and rvalue reference T&&). * However,

Why do we need reference collapsing rules [duplicate]

纵然是瞬间 提交于 2020-07-20 04:43:00
问题 This question already has answers here : Concise explanation of reference collapsing rules requested: (1) A& & -> A& , (2) A& && -> A& , (3) A&& & -> A& , and (4) A&& && -> A&& (2 answers) Closed 6 years ago . Everyone may know that we use rvalue-references combined with the reference collapsing rules to build perfect forwarding functions, like so template<typename T> void f(T&& arg) { otherfunc(std::forward<T>(arg)); } f(4); The reference collapsing rules are like +------+-----+--------+ | T

Why do we need reference collapsing rules [duplicate]

自闭症网瘾萝莉.ら 提交于 2020-07-20 04:42:49
问题 This question already has answers here : Concise explanation of reference collapsing rules requested: (1) A& & -> A& , (2) A& && -> A& , (3) A&& & -> A& , and (4) A&& && -> A&& (2 answers) Closed 6 years ago . Everyone may know that we use rvalue-references combined with the reference collapsing rules to build perfect forwarding functions, like so template<typename T> void f(T&& arg) { otherfunc(std::forward<T>(arg)); } f(4); The reference collapsing rules are like +------+-----+--------+ | T

Why do we need reference collapsing rules [duplicate]

↘锁芯ラ 提交于 2020-07-20 04:42:05
问题 This question already has answers here : Concise explanation of reference collapsing rules requested: (1) A& & -> A& , (2) A& && -> A& , (3) A&& & -> A& , and (4) A&& && -> A&& (2 answers) Closed 6 years ago . Everyone may know that we use rvalue-references combined with the reference collapsing rules to build perfect forwarding functions, like so template<typename T> void f(T&& arg) { otherfunc(std::forward<T>(arg)); } f(4); The reference collapsing rules are like +------+-----+--------+ | T

Is it true that “std::forward” and “std::move” do not generate code?

有些话、适合烂在心里 提交于 2020-06-29 06:43:21
问题 Is it true that "std::forward" and "std::move" do not generate code? I saw this saying in << An Effective C++11/14 Sampler >>. The related code is at the footnote. Could somebody explain the code in detail? I would be very grateful to have some help with this question. As per the documentation(https://gcc.gnu.org/onlinedocs/libstdc++/latest-doxygen/a00416_source.html), which says that: /** * @brief Forward an lvalue. * @return The parameter cast to the specified type. * * This function is

C++ Constructor: Perfect forwarding and overload

浪尽此生 提交于 2020-06-10 04:39:14
问题 I have two classes, A and B, and B is derived from A. A has multiple constructors (2 in the example below). B has one additional member to initialize (which has a default initializer). How can I achieve that B can be construced using one of the constructors of A without having to manually rewrite all the constructor overloads from A in B? (In the example below, I would otherwise have to provide four constructors for B: B():A(){} , B(string s):A(s){} , B(int b):A(),p(b){} , B(string s, int b)

C++ Constructor: Perfect forwarding and overload

六眼飞鱼酱① 提交于 2020-06-10 04:39:07
问题 I have two classes, A and B, and B is derived from A. A has multiple constructors (2 in the example below). B has one additional member to initialize (which has a default initializer). How can I achieve that B can be construced using one of the constructors of A without having to manually rewrite all the constructor overloads from A in B? (In the example below, I would otherwise have to provide four constructors for B: B():A(){} , B(string s):A(s){} , B(int b):A(),p(b){} , B(string s, int b)

std::move or std::forward when assigning universal constructor to member variable in C++

ぃ、小莉子 提交于 2020-01-29 10:44:25
问题 Consider the following classes foo1 and foo2 template <typename T> struct foo1 { T t_; foo1(T&& t) : t_{ std::move(t) } { } }; template <typename T> struct foo2 { foo1<T> t_; foo2(T&& t) : t_{ std::forward<T>(t) } { } }; Is it always the case that the constructor of foo1 represents the correct way to initialise the member variable T ? i.e. by using std::move . Is it always the case that the constructor of foo2 represents the correct way to initialise the member variable foo1<T> due to needing

Rvalue ref and perfect forwarding

时间秒杀一切 提交于 2020-01-24 06:01:48
问题 I've read few papers about && and I'm just curious if having: void fnc_1(int&& p) { //... } void fnc(int&& r) { fnc_1(r);//am I suppose to/should I? call it like so:fnc_1(std::forward(r)) } or just passing 'r' is enough? 回答1: fnc_1(r) won't compile, because r is an lvalue, just like any other variable, regardless of type. Yes, that's right, named rvalue references are lvalues, not rvalues. fnc_1(std::forward(r)) also won't compile, because std::forward is specifically designed not to infer

Rvalue ref and perfect forwarding

前提是你 提交于 2020-01-24 06:01:46
问题 I've read few papers about && and I'm just curious if having: void fnc_1(int&& p) { //... } void fnc(int&& r) { fnc_1(r);//am I suppose to/should I? call it like so:fnc_1(std::forward(r)) } or just passing 'r' is enough? 回答1: fnc_1(r) won't compile, because r is an lvalue, just like any other variable, regardless of type. Yes, that's right, named rvalue references are lvalues, not rvalues. fnc_1(std::forward(r)) also won't compile, because std::forward is specifically designed not to infer