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Date: Thu, 12 Feb 2015 17:15:24 +0100
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Subject: AW: [PHP-DEV] [VOTE] Scalar Type Hints
From: php@tutteli.ch ("Robert Stoll")

> -----Urspr=C3=BCngliche Nachricht-----
> Von: Nikita Nefedov [mailto:inefedor@gmail.com]
> Gesendet: Donnerstag, 12. Februar 2015 15:54
> An: Andrea Faulds
> Cc: Pavel Kou=C5=99il; PHP Internals
> Betreff: Re: [PHP-DEV] [VOTE] Scalar Type Hints
>=20
> Hi,
>=20
> 2015-02-12 18:31 GMT+04:00 Andrea Faulds <ajf@ajf.me>:
>=20
> > Hi Pavel,
> >
> > > On 12 Feb 2015, at 13:48, Pavel Kou=C5=99il <pajousek@gmail.com> =
wrote:
> > >
> > > C# does have dynamic typing.
> >
> > No it doesn=E2=80=99t, it=E2=80=99s a statically-typed language. I =
don=E2=80=99t understand
> > why you say it has dynamic typing - there is some limited dynamism =
in
> > parts, but I don=E2=80=99t think it affects what we=E2=80=99re =
talking about. Dynamic
> > typing and polymorphism aren=E2=80=99t the same.
> >
>=20
>  C# actually supports dynamic typing with a dynamic keyword [1]. But =
it really doesn't mean that having method
> overloading in a dynamic language is a good idea... C#, although it =
has a full ability to support dynamic typing, is not usually
> used in this fashion. To understand why it's not the best idea to use =
dynamic types with overloading you can just google
> "C# dynamic type with overloading site:stackoverflow.com".
>=20
> Another great deal in this question is performance, I think this =
subject was brought up a plenty of times in this ML and it
> was pointed out a couple of times that overloading even if doable at =
some point, would harm performance of method calls,
> which are already one of the slowest (if not the slowest) OPs in the =
engine. Languages like C# are usually able to resolve
> method references at compile time (unless virtual methods are used, =
even then it's only a matter of choosing right method
> from hierarchy not from all the overloaded variants).
>=20
> [1] https://msdn.microsoft.com/en-us/library/dd264736.aspx


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. 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):

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 ;)

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){
   //..
  }
  //...
}

With method overloading I could write the following, removing the hassle =
to write the dynamic dispatch myself:

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");
  }
}

Which is cleaner IMO.

Cheers,
Robert