Check if a variable type is iterable?

Question

Is there any way to check if an arbitrary variable type is iterable?

So to check if it has indexed elements or I can actually loop over it\'s children? (Use foreach

Answer 1

Or if (like me) you hate every SFINAE solution being a big block of dummy struct definitions with ::type and ::value nonsense to wade through, here's an example of using a quick and (very) dirty one-liner:

template <
    class Container,
    typename ValueType = decltype(*std::begin(std::declval()))>
static void foo(Container& container)
{
    for (ValueType& item : container)
    {
        ...
    }
}

The last template argument does multiple things in one step:

1. Checks to see if the type has a begin() member function, or equivalent.
2. Checks that the begin() function returns something that has operator*() defined (typical for iterators).
3. Determines the type that results from de-referencing the iterator, and saves it in case it's useful in your template implementation.

Limitation: Doesn't double-check that there's a matching end() member function.

If you want something more robust/thorough/reusable, then go with one of the other excellent proposed solutions instead.