There are three possible methods to create a Log
object. You can create a Log_ object directly
or call either the
&singleton() or the
factory()
method of the Log class.
Example 28-1. Initialization examples | // direct initialization of the 'file' container
$log = new Log_file('log.txt', 'identity text');
// initialization of the 'file' container through factory()
$log = &Log::factory('file', 'log.txt', 'identity text');
// initialization of the 'file' container through singleton()
$log = &Log::singleton('file', 'log.txt', 'identity text'); |
|
Directly initializing an instance of the Log is
probably the easiest method to understand.
The second two approaches make use of software engineering design
patterns (the "factory" and "singleton" metaphors).
Specifically, calling the factory() method will
create a new instance of one of the Log_
subclasses. The type of subclass that is returned is specified by the
first parameter (log_type) passed to the
factory() method. This approach effectively hides
the subclasses while still allowing the programmer to request a
concrete instance of a certain subclass. This is useful in cases where
the subclass type needs to be chosen at runtime.
The factory() method must always be called using
PHP's static method notation - Log::factory.
The singleton() method is identical to the
factory() method except that it guarantees that
only a single instance of the requested Log_
subclass exists. The singleton() method bases each
instance's uniqueness on the parameters used in the instance's
creation. In other words, only one instance with a given set of
creation parameters will ever be returned by the
singleton() method. The second invocation will
simply return a reference to the existing instance.
The singleton() method must also be called
statically. In addition, it requires PHP's reference notation -
&Log::singleton.
