C++ Primer, Fifth Edition

16.2.5. Template Argument Deduction and References

In order to understand type deduction from a call to a function such as

template <typename T> void f(T &p);

in which the function’s parameter p is a reference to a template type parameter T, it is important to keep in mind two points: Normal reference binding rules apply; and consts are low level, not top level.

Type Deduction from Lvalue Reference Function Parameters

When a function parameter is an ordinary (lvalue) reference to a template type parameter (i.e., that has the form T&), the binding rules say that we can pass only an lvalue (e.g., a variable or an expression that returns a reference ...