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Date: Thu, 12 Feb 2015 16:49:39 +0000
Cc: Nikita Nefedov <inefedor@gmail.com>,
 =?utf-8?Q?Pavel_Kou=C5=99il?= <pajousek@gmail.com>,
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To: Robert Stoll <php@tutteli.ch>
Subject: Re: [PHP-DEV] [VOTE] Scalar Type Hints
From: ajf@ajf.me (Andrea Faulds)

Hey Robert,

> On 12 Feb 2015, at 16:15, Robert Stoll <php@tutteli.ch> wrote:
>=20
> There are several programming languages which do support dynamic =
typing and method overloading somehow (Clojure, Erlang, Prolog, Cecil =
and certainly more).  Most of them use a multi-method approach and I =
think if PHP would introduce function/method overloading, then such an =
approach would be appropriate.

Interesting, I should maybe look into those. I=E2=80=99m not sure if all =
of those are really=E2=80=A6 =E2=80=9Cdynamic=E2=80=9D as such. Are you =
sure the overloading you=E2=80=99re referring to there isn=E2=80=99t =
pattern-matching?

> Right now, I need to implement the dynamic dispatching quasi myself =
which might be more verbose but is also more cumbersome (and uglier =
IMO). Consider the following (fictional example):
>=20
> I want to write a Logger-Service which provides one public method =
"log" which writes all kind of objects to a log. The corresponding =
classes do not all belong to my code base, are part of third party =
libraries respectively, so I am not able to introduce some interface =
which all classes implement. The strategy pattern is certainly a good =
idea for this problem but nevertheless, somewhere I need to have the =
distinction based on many if/else with instanceof (latest in the =
LoggerStrategyFactory) -- off topic, if someone has a better design =
approach to handle this problem, then let me know it in a private =
message, would be interesting as well ;)
>=20
> class Logger{
>  public function log($x){
>    if($x instanceof Foo){
>       logFoo($x);
>    }else if($x instanceof Bar){
>      logBar($x);
>    }
>    //...
>    }else{
>       throw new Exception("type ".gettype($x)." not supported");
>    }
>  }
>  private function logFoo(Foo $f){
>    //..
>  }
>  private function logBar(Bar $b){
>   //..
>  }
>  //...
> }
>=20
> With method overloading I could write the following, removing the =
hassle to write the dynamic dispatch myself:
>=20
> class Logger{
>  public log(){
>    $this->_log($x);
>  }
>  private function _log(Foo $f){
>    //..
>  }
>  private function _log(Bar $b){
>   //..
>  }
>  //...
>  private function _log($x){
>    throw new Exception("type ".gettype($x)." not supported");
>  }
> }
>=20
> Which is cleaner IMO.

We could also add some sort of pattern-matching syntax which could do =
the same thing, but would have usefulness beyond merely dispatching to =
multiple methods.

--
Andrea Faulds
http://ajf.me/