Re: Design by Contract

Hi Dmitry, On Tue, Feb 10, 2015 at 1:43 PM, Dmitry Stogov <dmitry@zend.com> wrote: > On Feb 9, 2015 11:20 PM, "Yasuo Ohgaki" <yohgaki@ohgaki.net> wrote: > > > > Hi Dmitry and Joe, > > > > On Mon, Feb 9, 2015 at 8:27 PM, Dmitry Stogov <dmitry@zend.com> wrote: > >> > >> yes. this may work. > >> probably better to put it after extends and implements. > >> > >> > >> Dmitry. > >> > >> On Mon, Feb 9, 2015 at 2:19 PM, Joe Watkins <pthreads@pthreads.org> > wrote: > >>> > >>> Could this be described as a requirement of the class ? > >>> > >>> class Mine > >>> require(invariant-expr) > >>> extends Something > >>> implements Someface { > >>> > >>> public function method($param) : return > >>> require(input-expr), > >>> return(output-expr) { > >>> > >>> } > >>> } > >>> > >>> To avoid invariant keyword maybe. > > > > > > This would work. > > If users have adopted DbC in some way, 'invariant' may be used already. > > > > I see two issues. > > > > Interface works, but most classes are class without interfaces. Then > users have to repeat > > require()/return() many times to check class state or have to use > interface for DbC. > > > > In D classes may have "invariant" constraints. We may use "require" > keyword for it. The constraints ineritance rules and order of calls to > constrains must be the same s in D. > > class Foo { > private $sum = 0; > require($this->sum >= 0); // invariant constraint will be called > before and after every method > function add($n) { > $this->sum += $n; > } > } > OK. I'll update the RFC. > > Since compiler does not know a method() is for DbC invariant, it will be > compiled and exists > > in production execution. > > > > Use of interface: > > - no additional keyword (pros) > > - requires interface for DbC, most classes does not require interface > (cons) > > - if interface is not used, user has to repeat invariant conditions > over and over (cons) > > - requires to define method that should not exist in production (cons) > > I didn't understand you idea. > Joe's idea was to use Interface for invariant condition grouping. If we use your idea, issue is solved. class Foo { > private $sum = 0; > require($this->sum >= 0); // invariant constraint will be called > before and after every method > function add($n) { > $this->sum += $n; > } > } > Ok. > > > > New keyword: > > - does not require interface for efficient definition (pros). > > - new keyword (cons) > > > > It seems we are better to choose proper keyword for 'invariant'. > 'invariant' is not common, so 'invariant' > > may be good enough choice. Does anyone use 'invariant' as > function/method/class/constant names? > > If there is better name, suggestion is appreciated. > > > > On place closure call like javascript is not supported in PHP, but > function works with assert. > > > > <?php > > function foo() { return FALSE; } > > assert(foo()); > > ?> > > PHP Warning: assert(): Assertion failed in - on line 3 > > > > This wouldn't be changed for require()/return()/invariant()? > > > > We need a switch to change development/production. I'll use "dbc=On/Off" > for now. > > If you have any better idea, please let me know. (dbc will be INI_SYSTEM) > > Check the "expectations" RFC. I think, it's going to be 3 state switch, > zero-cost disable, run-time disable, run-time enable. So, it may be > INI_ALL, but it won't be possible to switch from/to zero-cost at run-time. > Ok. > > > > For CLI, there will be no command line switch for dbc. It executes > script production mode by > > default. If user needs development mode > > > > php -d dbc=1 script.php > > > > should be used. > > > > > > And finally, are we going to allow custom assertion error message? e.g. > > > > require($a > 0, 'Parameter $a must be positive number'); > > I think, it may be useful. > Ok. I'll use it. > > > > Since this contract is definition like "implements"/"extends", we may > not allow > > custom error message. I'll write the RFC not to allow custom error > messages unless > > you dislike it. > > > > I think we have enough consensus/information to start writing the RFC. > > If I have any concern, I'll ask here. > > Ok, go forward :) > Updated wiki page. https://wiki.php.net/rfc/dbc2 If you would like to change something, please let me know. I don't think finished draft at all and I don't mind going back and forth. Regards, -- Yasuo Ohgaki yohgaki@ohgaki.net