Forwarding references in C++

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Forwarding references (also known as “universal references”) can bind to both lvalues and rvalues. The syntax is generally the same as rvalue references T&&, but they arise in two specific contexts: function template parameters, and auto declarations. Both cases have to deal with type deduction. Form must be T&& precisely, and type deduction must occur, otherwise T&& denotes an rvalue reference.

Example:

void f(Widget&& param);  // rvalue reference

auto&& var2 = var1;  // unversal reference

template<typename T>
void f(T&& param);       // universal reference