Re: Type hinting - Request for Discussion

Hi list. In advance, sorry for muddying the waters even further. Following the current discussion about typehints to primitives, I'm wondering if anyone have ever suggested to include some sort of user-land contract system, such as the one that exists in plt-scheme[1] Given the dynamic nature of php, I would suspect that it might be a much better fit. Unlike the semi-static typecheck that typehints can give, a contract system would be much more expressive and would add a lot more value (in my opinion anyway). I think part of the reason for the popularity of typehints is that it looks familiar for people coming from Java/C++/C#. The biggest challenge for such a contract system would then be to come up with something that doesn't look too alien. A simple way that I can think of is to overload the meaning of typehints so that they may either denote a class/interface (as they work currently) OR they may be a function which takes the variable as argument and yields a boolean. Eg.: function array_of_numeric($x) { foreach ($x as $val) { if (!is_numeric($val)) { return false; } } return true; } class Foo { /** Example use-case for a contract */ function sum(array_of_numeric $a) { return array_sum($a); } } This is just one suggestion - There are other ways to implement the concept. I can see a number of benefits to a contract system over the currently discussed typehint system: 1) It covers all the use cases for a type-based system (You can use is_integer as a contract, if you want that) 2) It's extensible in user-space, which means that it can be used to convey much more accurate information, relevant to the application needs. 3) It's focused on the interface of input-parameters, rather than their type. [1] http://docs.plt-scheme.org/guide/contracts.html -- troels