For some cases, by example when you works on webservices or an ETL, you can be a little lost between all the variables you use, specifically arrays.
I developed a derivative of the Hungarian notation to prefix my variables and find myself there. This notation can be applied in php, but also to any other languages, especially non-typed.
There is the prefixing I use with PHP variables in that specific cases, depending on their type and design :
Scalar types prefix
$i: int (unsigned)
$n: natural (signed int)
$fd: float round to 1 decimals
$fc: float round to 2 decimals
$fm: float round to 3 decimals
Non-scalar prefix types
$r: resource (PHP-specific)
Array, can be, by design, a collection of elements, or a single element. For me an “element” is an object-like data, stored as an associative array. While a collection if an array of elements.
So I can distinguish 3 different types for arrays :
$e: (array) Element (or Entry, or Entity) ; associative array containing data about an element.
$c: (array) Incremented Collection ; an array with auto-incremented keys containing elements. Means that the array keys don’t identify an element, event if the order to process it can be important.
$a: (array) Associative collection ; an array with associative & manually-assigned keys (like “hashes” in Perl ) containing elements.
For collections, I usually also put the variable in plural (or simply suffix with an s). I suggest to combine collection prefixes with the other prefix showing the values each entry contains :
$ca: incremented-collection of Associative collection
$cm: incremented-collection of mixed elements
$ae: associative-collection of array elements
$as: associative-collection of string elements
$am: associative-collection of mixed elements (each entry can contain different things)
$cbo: increment-collection of boolean OR objects. So we have to test if the entry is an object before processing it.
Semantic types :
$u: unsafe type or value, need to be checked or sanitized for security reason.
- Can be combined : ie
$usfor unsafe string, with possible code injection.
$zo: string of encoded object
$zj: string of encoded json
$zh: string of encoded html entities, ie: ‘"’
$ts: timestamp (signed int)
$d: date, format ‘Y-m-d’ (string)
$dt: datetime, format ‘Y-m-d H:i:s’ (string)
I personnally try to avoid to prefix private members / functions with underscores.