Section 9 -- bind -- Classes and Objects in PHP5 [9]

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Section 9-binding
In addition to restricted access, the access method also determines which method calls the quilt class or which attribute accesses the quilt class. the association between function calls and functions and the relationship between member access and variable memory addresses is called binding.
There are two main binding methods in computer languages: static binding and dynamic binding. static binding occurs between the data structure and the data structure, before the program is executed. static binding occurs during the compilation period, so you cannot use any runtime information. it targets the main body of function calls and functions, or blocks in variables and memory. because PHP is a dynamic language, it does not use static binding. however, static binding can be simulated.
Dynamic binding only uses available information during the runtime for access requests generated during the runtime. in object-oriented code, dynamic binding means deciding which method is called or which attribute is accessed. It is based on the class and not based on the access scope.
The actions of Public and protected members are similar to those of functions in the previous versions of PHP. Dynamic binding is used. this means that if a method accesses a class member that is overwritten in the subclass and is a subclass instance, the member of the subclass will be accessed (instead of accessing the member in the parent class ).
Let's take a look at example 6.10. This code output "Hey! I am Son. "because when PHP calls getSalutation, it is a Son instance that overwrites salutation in Father. if salutation is public, PHP will produce the same result. the operation of override method is similar. in Son, the identify call is bound to that method.
Even if the access method in the subclass is weakened from protected to public, dynamic binding still occurs. according to the principle of access method usage, it is impossible to enhance the access restrictions on class members. therefore, changing the access method from public to protected is impossible.
Listing 6.10 Dynamic binding
<? Php
Class Father
{
Protected $ salutation = "Hello there! "; // Greetings
Public function getSalutation ()
{
Print ("$ this-> salutationn ");
$ This-> identify ();
}
Protected function identify ()
{
Print ("I am Father. <br> n ");