What is STD forward?
std::forward has a single use case: to cast a templated function parameter (inside the function) to the value category (lvalue or rvalue) the caller used to pass it. This allows rvalue arguments to be passed on as rvalues, and lvalues to be passed on as lvalues, a scheme called “perfect forwarding.”
What is the point of std :: forward?
The idiomatic use of std::forward is inside a templated function with an argument declared as a forwarding reference , where the argument is now lvalue , used to retrieve the original value category, that it was called with, and pass it on further down the call chain (perfect forwarding).
How is STD forward implemented?
The implementation of std::forward template // For lvalues (T is T&), T&& std::forward(T&& param) // take/return lvalue refs. { // For rvalues (T is T), return static_cast(param); // take/return rvalue refs. }
What is universal reference?
Universal reference was a term Scott Meyers coined to describe the concept of taking an rvalue reference to a cv-unqualified template parameter, which can then be deduced as either a value or an lvalue reference.
What is a forwarding reference?
Forwarding reference (a.k.a Universal reference) — The mentioned type is a special type of reference that can bind anything & everything. i) Universal reference can mean both Rvalue reference and Lvalue reference. ii) May facilitate copying, may facilitate moving.
What do std :: move and std :: forward do?
std::move takes an object and casts it as an rvalue reference, which indicates that resources can be “stolen” from this object. std::forward has a single use-case: to cast a templated function parameter of type forwarding reference ( T&& ) to the value category ( lvalue or rvalue ) the caller used to pass it.
What does Decltype auto do?
decltype(auto) is primarily useful for deducing the return type of forwarding functions and similar wrappers, where you want the type to exactly “track” some expression you’re invoking.
What is perfect forwarding?
Perfect forwarding allows a template function that accepts a set of arguments to forward these arguments to another function whilst retaining the lvalue or rvalue nature of the original function arguments.
How do you do a forward reference?
Using an identifier before its declaration is called a forward reference, and results in an error, except in the following cases: When a goto statement refers to a statement label before the label’s declaration. When a structure, union, or enumeration tag is used before it is declared.
What are Rvalues?
An rvalue (so-called, historically, because rvalues could appear on the right-hand side of an assignment expression) is an xvalue, a temporary object or subobject thereof, or a value that is not associated with an object.
What is reference collapsing?
Reference collapsing is the mechanism that leads to universal references (which are really just rvalue references in situations where reference-collapsing takes place) sometimes resolving to lvalue references and sometimes to rvalue references.
What are rvalue references?
Rvalue references is a small technical extension to the C++ language. Rvalue references allow programmers to avoid logically unnecessary copying and to provide perfect forwarding functions. They are primarily meant to aid in the design of higer performance and more robust libraries.