help autocreating accessor methods

[dash2]

Hi,

I would like to autocreate accessor methods in a class, like this:

class Foo {
   // define some members...

foreach ($members as $member) {
    eval("
        function get_$member() {
            return(\$this->$member);
        }
    ");
}
}

This would work for pure functions, but when I try it within a class body, I either get a parse error, or I still get the class method as undefined.

Has anyone figured how to do this?

Ta

Dave

[website]

I don't under stand why they even allow this for basic functions, why would you ever want this?
besides, everything within a class must be either within a method or defenition of a variable.

[suntra]

See create_function().

But sincerely, I really don't see the use of what you try to do !

[dash2]

Create_function can create a function, but can it associate it with a particular class (so that it is accessible through inheritance etc.)? I read the user notes on php.net, but they only let you create a lambda function which is then accessible via a named method. I want to programmatically specify method names in the class, so that they can be inherited, overridden, etc.

The reason for creating accessor methods is a basic OO principle of not letting other classes mess with your data except through a defined interface. (Of course in PHP other classes always can mess with your data, but if you've provided them with a nice interface, at least they don't have an excuse!) The reason for autocreating accessor methods is that I don't want to write the same code for a class with 15 different fields!

Dave

[website]

well this simply doesn't fit, doing copy+paste or having many methods almost a like is exacly what OOP IS NOT about!

you should instead do get_member($member) or something like that!

[dash2]

Originally posted by website
well this simply doesn't fit, doing copy+paste or having many methods almost a like is exacly what OOP IS NOT about!

you should instead do get_member($member) or something like that!

I know what I am doing. ( Just about 😉 )

The reason I want to autocreate accessor methods, as stated in my previous post, was to avoid doing cut and paste. As for having many methods almost alike, normally that would be a problem because if you changed implementation you would have to rewrite the code many times. However, in this case, obviously, the methods are autocreated using the same single piece of code. A perl-ish example:

# code not tested
foreach $member (@members) {
    ${"Class::$member"}{SUB} = sub {
                my $this = shift;
		return $this->{$member};
    }
}

Another reason for creating member functions, rather than having single functions

get($member);

and

set($member, $value);

, is overriding. Suppose you want to ensure that a certain member in a subclass is only set to positive integers. With autocreated member functions, this is as simple as:

function set_member($value) {
    if (! ($value > 0)) die("Someone tried a non-positive value");
    parent::set_member($value);
}

With simple set() and get(), you have to add conditions.

// in subclass
function set($member, $value) {
  if ($member == 'member') {
    // do the checking...
  }
   parent::set($member, $value);
}

If you had many different members with different types of check, this would rapidly grow the length and complexity of the function.

HTH. HAND.

Dave

[website]

Originally posted by dash2
With autocreated member functions, this is as simple as:

function set_member($value) {
    if (! ($value > 0)) die("Someone tried a non-positive value");
    parent::set_member($value);
}

With simple set() and get(), you have to add conditions.

// in subclass
function set($member, $value) {
  if ($member == 'member') {
    // do the checking...
  }
   parent::set($member, $value);
}

[/B]

I do not agree, or I do not understand.
If you autocreate some method, you are creating the same set of conditions for all the methods you create, that is equalent to setting the condition in the single set() function as in both cases it does affect all cases of setting the member variables...

I hope you understand what I am trying to say...

[dash2]

The original method is the same for all different members, but you can subclass it differently.

For example, suppose you have a class with fields foo, bar and baz. You autocreate accessors and mutators in the class. So now you have get_foo(), get_bar() and get_baz(), as well as set_foo(), set_bar() and set_baz(). All the get methods are identical with one another, and so are the set methods.

Now you create a subclass of the original class. In the subclass, you have fields foo, bar and baz as before, and you already have accessor and mutator methods for those provided by the superclass. You also have the field bod, which you want to limit to positive integers (or whatever).

The superclass autocreates set_bod() and get_bod()methods (I am assuming that methods are autocreated the first time an object is created, so subclasses share this automatic functionality), but you can override the set_bod()method, as described above, to do checks before calling parent::set_bod().

If you just had generic set() and get() methods, you'd have to override the generic set() method in the subclass, and insert a condition: if ($field == 'bod'). This makes your code more complex, especially if there are many different fields and different types of check.

Dave

[website]

It depends, ofcourse if you have $bob and $nob and they don't hold similar data, they should ofcourse have seperate get and set methods, if you have as in your first example, an array, called $members, all is the same, they are all members even if they have differant names etc. so in reply to your first post I would have it setMember() and getMember($memberid)
the get method would look up the key of the array that holds $memberid and the setMember() would add to the array...

If you have variables $database and $client they should defenatly not use the same set() and get() methods because they are not similar, but you would never have some huge amount of these 'unique' variables in each class

The superclass autocreates set_bod() and get_bod()methods (I am assuming that methods are autocreated the first time an object is created, so subclasses share this automatic functionality), but you can override the set_bod()method, as described above, to do checks before calling parent::set_bod().

This I find little wierd, does the super class create the set/get method for a varibles defined in the subclass ?

Anyhow, I am enjoying this converstion 🙂 Keep posting.

[dash2]

Originally posted by website




This I find little wierd, does the super class create the set/get method for a varibles defined in the subclass ?

Anyhow, I am enjoying this converstion 🙂 Keep posting.

Yes, ideally you would do this. Again in Perl you would have an array of variables defined in each class, and the class initialisation method would check this array: foreach (@{$class . '::members'}) {#create methods}.

But I still want to know, can you do this in PHP?

[website]

No, I don't think this can be done with PHP and I don't see why it should be needed.