Posted by David Haynes on 06/25/06 13:26

Tim Van Wassenhove wrote:
> On 2006-06-25, David Haynes <david.haynes2@sympatico.ca> wrote:
>> PHP5 has weak polymorphism but not true polymorphism in the sense that
>> it is used in OOP.
>
> So how would you define polymorphism? And what exactly are the
> differences between 'weak' and 'true' polymorphism?
>
> If i look at http://en.wikipedia.org/wiki/Polymorphism_%28computer_science%29
>
> "The concept of polymorphism applies to data types in addition to
> functions. A function that can evaluate to and be applied to values of
> different types is known as a polymorphic function. A data type that
> contains elements of different types is known as a polymorphic data
> type."

Keep reading the article you referenced.

"This type of polymorphism [overloading] is common in object-oriented
programming languages, many of which allow operators to be overloaded in
a manner similar to functions (see operator overloading). It is also
used extensively in the purely functional programming language Haskell
in the form of type classes. Many languages lacking ad-hoc polymorphism
suffer from long-winded names such as print_int, print_string, etc. (see
C, Objective Caml)."

>> function __construct($one, $two="two", $three="three") {
>>
>> I cannot instantiate this object as new Foo($one, $three) since there is
>> no typing on the arguments and, therefore, no signature for a 'one,
>> three' contructor.
>
> Imho that's the same as saying: I'm standing with my back against a wall,
> and now i'm wondering why i can't step backwards anymore...
>
> Define your constructor as __constructor($args) and handle with
> func_num_args and func_get_args(s) any number of parameters...
>
> (I do agree that the language/compiler can, probably should, make this
> easier... But that's a different discussion.)

What you have specified is a non-overloaded generic constructor. I view
this as a work-around due to the inability of the PHP interpreter to
handle overloading polymorphism.

I'm not saying that this is a bad thing - in fact if you rewind your
news feed about a week - you will see that I recommended such an
approach to another coder, but I am saying that most strongly-typed OO
languages do support overloading as part of the their OOP environment.

-david-

[Back to original message]