String - array ambiguity in PHP

Question

I vaguely remember, starting with the first readings of PHP documents (more than 10 years ago) that syntax like an array for accessing characters in arrays ( $string[0] ) caused some ambiguity or undefined behavior.

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

To solve the problem of ambiguity between strings and arrays, a new syntax was introduced to dereference individual characters from strings:

$string{2}

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

I understand that $string[2] can be confusing, but I'm not sure how this can be ambiguous?

Also: I'm curious how the new $string{2} syntax removes ambiguity / confusion, given that curly braces ( obviously ) also work for "real" arrays.

Answer 1

The only ambiguity is that if you expect an array, but actually have a string, $var[0] will provide you with the first byte of the string instead of the first element of the array. This can lead to a big crash in the head and wonder why PHP gives you only the first character and not the whole array. This is even more true for non-numeric indices like $var['foo'] , which actually works if $var is a string (yes, please don't ask). That is, it can make debugging a little more difficult if your program is primarily faulty.

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

Answer 2

Many problems caused by the ambiguity between line offsets and array offsets have been removed with the changes in 5.4, which are after the publication date of your link. http://php.net/manual/en/migration54.incompatible.php

For this reason, I recommend [] for line offsets in new code.

Answer 3

Well, I checked some variables with this code:

 <pre><?php dumpling(array("php")); dumpling(array()); dumpling(0); dumpling(1); dumpling(TRUE); dumpling(FALSE); dumpling(NULL); dumpling("php"); function dumpling($var){ var_dump($var[0]); var_dump($var{0}); } ?> 

and there was no difference between them.

The output was:

 string(3) "php" string(3) "php" NULL NULL NULL NULL NULL NULL NULL NULL NULL NULL NULL NULL string(1) "p" string(1) "p"