Type hinting for PHP 5.3

For a few years now at work we've been using a patched version of PHP, one those patching featuring type hinting. Over time this proved to be a very handy feature that allows for a much more readable code and introduces a language based validation layer to ensure that the right data types are getting to your functions and methods. It also caught numerous bugs due to functions returning or passing un-expected values. Best of all this feature does not require any changes on the part of opcode caches (essential component for PHP performance) and allows for simple deployment.

I and other people have tried a number of times in the past to introduce type hinting into stock PHP, but unfortunately have never been successful. On a general level most people agree it would be a good idea to have, since it is an optional feature and does not introduce any regressions, heck you can even mix type hinted code with the non-type hinted one. The "PROBLEM" has always been combining of PHP's typeless nature with type hinting, which is where the consensus has been difficult (impossible) to reach. To illustrate the problem let's consider the following:

function foo(int $bar) {}

Some people would expect that passing "1" (string containing number 1) would be accepted by function foo() and not raise any type errors, since in PHP typically, numbers within strings are considered to be perfectly valid numbers ("1" + "1" == 2). Hence the conflict, some people (I am a part of that group) think that type hinting should be strict, while others think it should be more permissive to be inline with PHP's fluid nature.

With introduction of PHP 5.3 and free day in the middle of the week (Happy Canada Day to all Canucks) I've decided to port my internal patch to 5.3 and introduce a new 'feature' to it to hopefully bridge the divide. I've added a IS_NUMERIC (numeric) type hint that allows the script author to designate a parameter as having to be number, meaning input of type boolean, long or float as well as strings containing purely numbers will be accepted. This means if were to rewrite my previous function as:

function foo(numeric $bar) {}

Then calling foo("112"); would perfectly valid. To further extend basic type hinting support I've also added IS_SCALAR (scalar) type hint that allows a parameter to be designated as scalar, which means it'll accept any boolean, float, string or integer value.

The patch is available here: http://ia.gd/patch/type_hint_53.txt

I've also posted it to the internals list in the hope of gathering enough support on the part of PHP developers and users to have it added to 5.3 and future releases of PHP.

It should be noted that this is not the first idea for type hints, that credit goes to Hannes Magnusson who had posted a similar patch on the internals list back in 2006. Also, back in 2008 Felipe Pena wrote a complete RFC on type hinting with patches and even test.