Can someone explain this code?

Flicking through the O'Reilly C++ Quick Reference I saw a snippet of code that I didn't understand at all because I've never seen anything like it before:

Code:

---

for SpectrumColor operator++(SpectrumColor &s, int dummy)
{
    return s = (s >= Violet) ? Red : SpectrumColor(s + 1);
}

---

SpectrumColor is an enumeration as you've probably guessed. I just don't understand this form of the for loop because I've never seen it.

It looks like a typographical error: without the for, it would just be a non-member postfix operator++.

Also, it seems that it is operator++ for an enum:

Code:

---

#include <iostream>
enum SpectrumColor { Red, Orange, Yellow, Green, Blue, Indigo, Violet };

SpectrumColor operator++(SpectrumColor &s, int dummy)
{
    return s = (s >= Violet) ? Red : SpectrumColor(s + 1);
}

int main()
{
    SpectrumColor col = Blue;
    col++;
    std::cout << col << ' ';
    col++;
    std::cout << col << '\n';
    col++;
    std::cout << col << '\n';
}

---

Aha, I'd hoped it was an error because it sure as hell didn't look like anything that made sense to me with that "for." Here I was worrying that I'd skipped a couple of chapters.

Well, I guess I'll check the website for the errata.