PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

190 Chapter 6 Object-Oriented PHP
The ObjectIterator class has a set of functions as required by the Iterator interface:
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The constructor is not required but is obviously a good place to set up values for
the number of items you plan to iterate over and a link to the current data item.
The rewind() function should set the internal data pointer back to the beginning
of the data.
The valid() function should tell you whether more data still exists at the current
location of the data pointer.
The key() function should return the value of the data pointer.
The value() function should return the value stored at the current data pointer.
The next() function should move the data pointer along in the data.
The reason for using an iterator class like this is that the interface to the data will not
change even if the underlying implementation changes. In this example, the
IteratorAggregate class is a simple array. If you decide to change it to a hash table or
linked list, you could still use a standard Iterator to traverse it, although the Iterator
code would change.
Converting Your Classes to Strings
If you implement a function called __toString() in your class, it will be called when
you try to print the class, as in this example:
$p = new Printable;
echo $p;
Whatever the __toString() function returns will be printed by echo.You might, for
instance, implement it as follows:
class Printable
{
public $testone;
public $testtwo;
public function __toString()
{
return(var_export($this, TRUE));
}
}
(The var_export() function prints out all the attribute values in the class.)
Using the Reflection API
PHP’s object-oriented features also include the reflection API. Reflection is the ability to
interrogate existing classes and objects to find out about their structure and contents.
This capability can be useful when you are interfacing to unknown or undocumented
classes, such as when interfacing with encoded PHP scripts.
The API is extremely complex, but we will look at a simple example to give you
some idea of what it can be used for. Consider the Page class defined in this chapter, for