I'm sorry, the expected result and actual result got mixed up when I was submitting. Expected is actual, and actual is expected.

return $key > 0 ? $this->a[$key] : $this->b[$key];

is the same as

return ($key > 0 ? $this->a[$key] : $this->b[$key]);

C is not comparable because it has only pass and return by value.

This is documented in http://pt.php.net/ternary :

Note: Please note that the ternary operator is a statement, and that it doesn't evaluate to a variable, but to the result of a statement. This is important to know if you want to return a variable by reference. The statement return $var == 42 ? $a : $b; in a return-by-reference function will therefore not work and a warning is issued in later PHP versions.

See also http://stackoverflow.com/questions/3389928/can-you-pass-by-reference-while-using-the-ternary-operator/3390182#3390182

Thank you for pointing me to that article, it's strangely placed in the chapter on Comparison operators, which Conditional operator isn't, so I haven't found it in the first place.

Well, although C does have pointers, what I meant was C++, which has references and ternary operator works with them. This code is perfectly valid and outputs 20, as expected:

#include <iostream>
using namespace std;

class test {
  public:
  int i, j;
  test():i(8),j(10){}
  int& a(int b) {
    return b == 2 ? i : j;
  }
};
int main() {
  test my;
  int& a = my.a(2);
  a += 12;
  cout << "Weekly Hours: " << my.a(2) << endl;
  return 0;
}

So, I still find it hard to follow the PHP logic in this. "the ternary operator is a statement, and that it doesn't evaluate to a variable, but to the result of a statement." -- but result of a statement is a variable. I suppose this has to do with some PHP internal specifics, which I am not aware of. But if this use of ternary operator doesn't work and produces a wrong result, then surely it should be a warning, not a notice.

But in any case, thank you again for your feedback, I'm mostly writing this comment for people who might research this subject in the future, maybe deciding to improve things, and I've no intentions to offend anyone in any way.