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Date: Mon, 9 Feb 2015 14:52:19 +0900
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To: "guilhermeblanco@gmail.com" <guilhermeblanco@gmail.com>
Cc: Joe Watkins <krakjoe@php.net>, Stanislav Malyshev <smalyshev@gmail.com>, 
	Dmitry Stogov <dmitry@zend.com>, PHP Internals <internals@lists.php.net>
Content-Type: multipart/alternative; boundary=089e014953ecf2b9b5050ea16141
Subject: Re: [PHP-DEV] Design by Contract
From: yohgaki@ohgaki.net (Yasuo Ohgaki)

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Content-Type: text/plain; charset=UTF-8

Hi Guilherme,

On Mon, Feb 9, 2015 at 1:44 PM, guilhermeblanco@gmail.com <
guilhermeblanco@gmail.com> wrote:

> Class invariants could be done as this example:
>
> class Foo {
>     private function isValidState() {
>         // Checks class's state and returns boolean
>     }
>
>     public function doSomething($args) {
>         // Some complex operation over Foo instance using $args
>         // then...
>
>         assert $this->isValidState(): $this; // it would call
> Foo::__toString() for AssertionError message
>     }
> }
>
> Another example of pre and post conditions:
>
> function foo($number) {
>     // pre-condition
>     assert is_numeric($number): '...';
>
>     // Some expensive operation creating $value as response
>
>     // post-condition
>     assert someCheckWith($value): '...';
>     return $value;
> }
>
> A good explanation about use-cases can be found here
> http://docs.oracle.com/javase/8/docs/technotes/guides/language/assert.html#class-invariants
>

Thank you for the info.

I had this syntax in mind.

class Foo {
   __invariant() {
      // Ignored for production.
      // Check class state, every method calls invoke this method
before/after except
      //  __construct()/__wakeup()/__set_state() - after only
      //  __destruct() - before only
   }
}

// Framework developer shouldn't use this. Leave this function for app
developers.
function __invariant() {
  // Ignored for production.
  // Invariant conditions of functions invoked for every function calls
  // to check app state. e.g. global vars,etc
}

__invariant() has similar issue as __autoload(), we may be better to
provide generic registration
method.

Just my initial thought for discussion.

Regards,

--
Yasuo Ohgaki
yohgaki@ohgaki.net

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