Declaring a Class

To design your program or code library in an object-oriented fashion, you’ll need to define your own classes, using the class keyword. A class definition includes the class name and the properties and methods of the class. Class names are case-insensitive and must conform to the rules for PHP identifiers. The class name stdClass is reserved. Here’s the syntax for a class definition:

class classname [ extends baseclass ] [ implements interfacename ,
    [interfacename, ... ] ]
  [ use traitname, [ traitname, ... ]; ]

  [ visibility $property [ = value ]; ... ]

  [ function functionname (args) {
    // code

Declaring Methods

A method is a function defined inside a class. Although PHP imposes no special restrictions, most methods act only on data within the object in which the method resides. Method names beginning with two underscores (__) may be used in the future by PHP (and are currently used for the object serialization methods __sleep() and __wakeup(), described later in this chapter, among others), so it’s recommended that you do not begin your method names with this sequence.

Within a method, the $this variable contains a reference to the object on which the method was called. For instance, if you call $rasmus->birthday(), inside the birthday() method, $this holds the same value as $rasmus. Methods use the $this variable to access the properties of the current object and to call other methods on that object.

Here’s a simple class definition of the Person class that ...

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