The range-based for statement

is equivalent to

where

• if the for-range-initializer is an expression, it is regarded as if it were surrounded by parentheses (so that a comma operator cannot be reinterpreted as delimiting two init-declarators);
• range, begin, and end are variables defined for exposition only; and
• begin-expr and end-expr are determined as follows:

  • if the type of range is a reference to an array type R, begin-expr and end-expr are range and range + N, respectively, where N is the array bound.

    If R is an array of unknown bound or an array of incomplete type, the program is ill-formed;

  • if the type of range is a reference to a class type C, and searches in the scope of C ([class.member.lookup]) for the names begin and end each find at least one declaration, begin-expr and end-expr are range.begin() and range.end(), respectively;

  • otherwise, begin-expr and end-expr are begin(range) and end(range), respectively, where begin and end undergo argument-dependent lookup ([basic.lookup.argdep]).

[Example 1: int array[5] = { 1, 2, 3, 4, 5 }; for (int& x : array) x *= 2; — end example]

[Example 2: using T = std::list<int>; const T& f1(const T& t) { return t; } const T& f2(T t) { return t; } T g(); void foo() { for (auto e : f1(g())) {} // OK, lifetime of return value of g() extended for (auto e : f2(g())) {} // undefined behavior } — end example]