What is “for (x : y)”?

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C++11 introduced a new iteration statement, the so-called range-based for loop. It differs from the ordinary for loop in that it only gives you access to the members of a range, without requiring you to name the range itself explicitly and without using proxy iterator objects. Specifically, you are not supposed to mutate the range during the iteration, so this new loop documents the intent to “look at each range element” and not do anything complicated with the range itself.

The syntax is this: for (decl x : r) { /* body */ }, where decl stands for some declaration and r is an arbitrary expression. This is functionally mostly equivalent to the following traditional loop:

{
    auto && __r = r;

    using std::begin;
    using std::end;

    for (auto __it = begin(__r), __e = end(__r); __it != __e; ++__it)
    {
        decl x = *it;
        /* body */
    }
}

As a special case, arrays and braced lists are also supported natively.

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