Use class variables when only access is local?

bunner_bob

Is there any reason to use class variables (i.e. '$this->variable') rather than 'local' variables (i.e. '$variable') in cases where the variable is only accessed within a single class method?

It seems that unless you need to:
a: assign a value to a variable from outside the class:

$foo = &new Foo;
$foo->var = 'the monkey';

b: reference a variable outside the class, so you can alter a value without returning something from a method

$title = 'old title';

$foo = &new Foo;
$foo->title = &$title;
$foo->changeTitle('new title'); // method sets new value for $this->title inside Foo class

or
c: refer to the variable from multiple methods inside a class

you're best off just creating the variable locally inside the method and using it as needed - $variable instead of $this->variable.

Is there an advantage, or a best-practices dictate, that says I should use $this->variable when there's no immediately apparent logical reason for it?

Roger_Ramjet

'Best practice' sez that you should limit the scope of a variable to only that which is neccessary. So if a var is only used/needed within a method limit it's scope only to that method.

As far as objects go, none of their raw data:variables should be directly addressable from outside the object, but only through properties and methods.

tomhath

An object variable will keep it's value after the method returns so you can use it again next time. A local variable goes away when it goes out of scope (unless it's declared static). As Roger said, limit the scope (and persistence) to what's necessary.

bunner_bob

OK - so what seems to make sense is actually the right way to do it - love it when it works out that way.

Originally posted by Roger Ramjet
As far as objects go, none of their raw data:variables should be directly addressable from outside the object, but only through properties and methods.

Not entirely clear what you mean here. What I think you're saying is, if you want to change a local variable inside an object, you should do it via a class method or by assigning a value to a property (via $class->property). But how else COULD you do it? I suppose only if you made the variable global - or is there another way? Not that I want to do it, of course. I want to NOT do it, if I shouldn't 🙂

(I'm also trying to figure out why I posted this in 'Database' instead of 'Coding' - sorry!)

tomhath

Php lets you refer to object variables from outside the class declaration:

<?php
  class LazyWay {
    var $class_var = 'a';
  }

  $a = new LazyWay();
  $a->class_var = 'b';
  echo $a->class_var;
?>

Some languages absolutely prohibit this, some let you decide whether the class members are public, private, etc.

http://java.sun.com/docs/books/tutorial/java/javaOO/accesscontrol.html

Other languages like VB use a sort of compromise called properties:

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vbenlr98/html/vastmpropertyget.asp

Which way is correct can become a religious war. Here's a famous quote on how the designers of Perl feel about it:

      "Perl does not enforce private and public parts of its
       modules as you may have been used to in other languages
       like C++, Ada, or Modula-17.  Perl doesn't have an
       infatuation with enforced privacy.  It would prefer that
       you stayed out of its living room because you weren't
       invited, not because it has a shotgun."
                -- Man page for perlmodlib.