Re: [PHP-DEV] "::" meaning and documentation From: waldschrott (waldschrott <email protected>)
Date: 07/04/00

<applause/>
that adresses all we discussed about in "[PHP-DEV] Class::? - accessing
data, no success..." and more, I´d take the entire mail as an enhancment
report!

regards

> How it _should_ work, if PHP was to behave similarly to
> other OO languages:
>
>
> Uses of :: in an instance
> =========================
>
> Using :: on instance functions
> ------------------------------
>
> If used in an instance of a class, :: should be able
> to address a shadowed method in a superclass of the
> current instances class. That is,
>
> class a {
> function somef() {
> print "I am somef() in a\n";
> }
> }
>
> class b extends a {
> function somef() {
> print "I am somef() in b\n";
> }
>
> function otherf() {
> $this->somef(); // will print "I am somef in b"
> a::somef(); // will print "I am somef in a"
> }
> }
>
> $b_instance = new b;
> $b_instance->somef(); // will print "I am somef in b"
>
> This is useful to address a shadowed instance method
> in a superclass of a class, for example when extending
> an initalizing function. Note how the name of the
> superclass is mentioned multiple times in b, which is
> a denormalization. Changing the name of a classes superclass
> will make changed in many code locations necessary.
>
> It would be much more elegant if you had a pseudo variable
> $super instead which could be used to reference a classes
> superclass as in
>
> class b extends a {
> function somef() {
> print "I am somef() in b\n";
> }
>
> function otherf() {
> $this->somef(); // will print "I am somef in b"
> $super->somef(); // will print "I am somef in a"
> }
> }
>
> Alternatively, it would be useful if the class and
> function names around a T_PAAMAYIM_NEKUDOTAYIM need
> not be T_STRING, but can be variable references,
> facilitating syntax like
>
> class b extends a {
> function somef() {
> print "I am somef() in b\n";
> }
>
> function otherf() {
> $c = get_parent_class(); // returns (string) "a"
>
> $this->somef(); // will print "I am somef in b"
> $c::somef(); // will print "I am somef in a"
> }
> }
>
>
> Using :: on instance variables
> ------------------------------
>
> This could be used to address shadowed instance variables
> as well, but the concept of "shadowed instance variable"
> is only useful when you consider static initalizers of
> instance variables. That is, consider
>
> class a {
> var $some_var = "initializer in a";
> }
>
> class b extends a {
> var $some_var = "initializer in b";
>
> function showvar() {
> print $this->some_var; // will print "initializer in b"
> print a::some_var; // will print "initializer in a"
> }
> }
>
> That would be sensible, but if it doesn't work that way,
> it is of little importance.
>
>
> Uses of :: outside of an instance
> =================================
>
> Class functions
> ---------------
>
> Outside of an instance, :: does make sense only to address
> (Objective C name:) class functions alias (Java name:)
> static class member functions and (Objective C name:)
> class variables alias (Java name:) static class member variables.
>
> A class function/static class member function is a function
> which can be called in a class even when no instance of
> that class is available. Such functions are useful for a
> variety of purposes (see any Objective C runtime documentation
> or any Java handbook), but they can be emulated with plain
> functions (raising namespace issues).
>
> Example use:
>
> class a {
> function sfunction() {
> print "I am sfunction in a\n";
> }
> }
>
> a::sfunction(); // will print "I am sfunction in a"
>
> A class function should be able to call other class functions,
> but cannot call instance functions and therefore not refer to
> $this, as there is no instance. It is of little use to create
> a default instance (of a default class), raising an error
> condition would be more sensible.
>
> Class variables
> ---------------
>
> A class may have class variables. Such variables are useful to
> keep track of all instances of a class, for example a database
> class keeping track of all database links in all database class
> instance objects, or for example a Drawable class, keeping track
> of all Drawable instances and providing a draw_all() class
> function.
>
> This can be emulated using a Keeper class with a single
> instance and putting all instances into the Keeper after creation,
> but having it in a class would still be useful in some cases.
>
> class a {
> var $class_var;
> }
>
> a::class_var = 10;
>
> Assorted problems
> =================
>
> :: outside of classes introduces problems with variable interpolation,
> as the construct is no longer introduced by $ signs. This leads at least
> to strange syntax and may be creating other, more serious problems as
> well.
>
> In Smalltalk and in Objective C, classes are objects, too. Their
> class is named "Metaclass" and Metaclass implements a number of
> standard functions for dealing with Classes. An instance of
> Metaclass is a class, and belongs to the class Metaclass as well,
> terminating this recursion.
>
> That is, in Objective C and Smalltalk
>
> $o = new SomeClass; // $c is an instance of the class SomeClass
> print $o->get_class_name(); // will print SomeClass
>
> $c = $o->get_class(); // does not return a string, but an object
> // which is the class SomeClass.
> print $c->get_class_name(); // will print MetaClass
>
> $m = $c->get_class(); // does return the class object for $c,
> // which is the MetaClass object
> $m->get_class(); // will print MetaClass, also.
>
>
> Somehow a similar Semantic should be defined for PHP4 as well. It
> need not be identical, but it should be defined to clear things up.
> And it should be defined in a way that makes things function in
> a sensible way (not just "because the implementation happens to be
> this way").
>
> Kristian
> 

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