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| Code | |||||
Here`s the deal. First thing to realize is that PHP code (that is, code blocks inside PHP tags) has two very distinct modes - regular code, and code inside double quotes (there`s also code inside single quotes and backticks, but let`s skip this for now). With regular code, associative indices are any valid string expression. That means a variable that contains a string, a string literal (e.g. "foo") or some `complex` string expression like $a."foo" or the likes. Labels, such as foo (without any surrounding quotes) are no longer considered valid string literals (as of PHP 3.0RC5). Such labels are used for constants, even though if you use foo, and foo isn`t a valid constant, the label would be evaluated to the string expression "foo" (and would also generate a notice-level warning). To summarize, with regular code, you should use $array["foo"] instead of $array[foo], even though both would work. If foo is a constant, the 2nd format has a different meaning from the 1st (e.g. if foo==2, $array[foo] is identical to $array[2]). Inside quoted strings, PHP supports a much much more limited range of the array variable references available in regular code. PHP 3.0 supports the following formats inside quoted strings, nothing more, nothing less: $a[7] 7 can be any valid number $a[label] label can be any valid label, e.g. foo $a[$b] $b can be any simple scalar variable The following notation is also available to prevent certain ambiguities under certain circumstances: ${a[7]} ${a[label]} ${a[$b]} Now, the interesting part here is that when you want to access an associative index inside a quoted string, you have only two options - use a variable as an index (e.g. $b=="foo", $a[$b] == $a["foo"]), or, use a label, like foo. Using "foo" explicitly will NOT work. Among other things, this means that not all associative indices can be explicitly accessed inside quoted strings (e.g., $array["foo bar"] cannot be directly accessed inside quoted strings, unless you have a scalar variable that contains the string "foo bar"). So, to extend the summary, inside quoted strings, you would normally access associative arrays using $a[foo]. Future considerations --------------------- I guess mostly everybody wants to write code that`ll be compatible with future versions of PHP 3.x, namely version 3.1. None of us (core developers) knows what exactly PHP 3.1 would look like, even though we have plenty of ideas for it. Improving on the variable reference parsing inside quoted strings is one of the things that`s scheduled for PHP 3.1. We haven`t yet decided how the behavior would be exactly, but in order to write safe code that would work under future PHP versions, it`d probably be wise to follow the following guidelines for array references inside quoted strings: * For simple associative indices, use the simple $foo[bar] notation. * Avoid using ${foo[bar]}. The general idea in PHP 3.1 is to enable full-featured parsing inside the curly braces, which means foo would be considered a constant rather than the string literal "foo". * For `complex` array references, or ambiguous array references (i.e. ones that require the ${foo[bar]} notation), use the concatenation operator, e.g. "abcdefg" . $foo["bar"] . "hijklmnop" - this format will definitely remain intact in future PHP versions. A bit long, but I hope it helps. | |||||
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