Is constexpr really needed?

Question

I have been looking at the new constexpr feature of C++ and I do not fully understand the need for it.

For example, the following code:

Answer 1

int MaxSize() {
    ...

    return ...; }

static const int s_maxSize = MaxSize();

int vec[s_maxSize];

No, it can't. That's not legal C++03. You have a compiler extension that can allocate variable-length arrays.