string - array ambiguity in PHP

Question

I dimly recall, from my first readings of the PHP docs (more than 10 years ago) that the array-like syntax to access characters in arrays ($string[0]) posed some ambiguity or undefined behaviour.

The O'Reilly PHP Pocket Reference (2nd ed) states:

To solve an ambiguity problem between strings and arrays, a new syntax has been introduced to dereference individual characters from strings:

$string{2}

This syntax is equivalent to $string[2], and is preferable.

I understand that $string[2] might be confusing, but I'm not sure how it could be ambiguous?

Furthermore: I wonder how the new syntax $string{2} removes the ambiguity/confusion, considering that the curly braces (apparently) also work for "real" arrays.

Answer 1

The only ambiguity is that if you're expecting an array, but actually have a string, $var[0] will give you the first byte of the string instead of the first array element. This may lead to a lot of head scratching and wondering why PHP is only giving you the first character instead of the whole array element. This is even more true for non-numeric indexes like $var['foo'], which actually works if $var is a string (yeah, please don't ask). I.e. it may make debugging slightly more difficult if your program is wrong in the first place.

There's no ambiguity for correct programs, since a variable cannot be a string and an array at the same time.