c++ - What does (&) -- ampersand in parentheses -- mean in this code? -

in this answer, following code given (c++11):

template <typename t, size_t n> constexpr size_t size_of(t (&)[n]) {     return n; } 

what (&) mean in context? sort of thing exceptionally difficult search for.

it's shorthand this:

template <typename t, size_t n> constexpr size_t size_of(t (&anonymous_variable)[n]) {     return n; } 

in function, don't need name of variable, template deduction on n - can choose omit it. parentheses syntactically necessary in order pass array in reference - can't pass in array value.