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This article is about how to bind PHP5.0 dynamically and why the class members of private simulate static binding. The editor thinks it is very practical, so I share it with you. I hope you can get something after reading this article.

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 at compile time, so you cannot take advantage of any runtime information. It targets the function call and the body of the function, or the variable and the block in memory. Because PHP is a dynamic language, it does not use static binding. But you can simulate static binding.

How to bind PHP5.0 dynamically

Dynamic binding uses only the information available at run time for access requests generated at run time. In object-oriented code, dynamic binding means determining which method is called or which property is accessed, based on the class itself and not on the access scope.

The actions of Public and protected members are similar to those of functions in previous versions of PHP, using dynamic binding. This means that if a method accesses a class member that is overridden in a subclass and is an instance of a subclass, the member of the subclass will be accessed (rather than the member of the parent class).

Look at example 6.10. This code outputs "Heyweight IamSon." Because when PHP calls getSalutation, it is an instance of Son and overwrites the salutation in Father. If salutation is public, PHP will produce the same result. The operation of the override method is similar. In Son, the call to identify is bound to that method.

Even if the access mode in the subclass is weakened from protected to public, dynamic binding still occurs. According to the principle of access mode use, it is impossible to strengthen the access restrictions on class members, so it is impossible to change the access mode from public to protected.

Listing6.10Dynamicbinding dynamic binding

ClassFather

{

Protected$salutation= "Hellothere!"; / / greetings

PublicfunctiongetSalutation ()

{

Print ("$this- > salutationn")

$this- > identify ()

}

Protectedfunctionidentify ()

{

Print ("IamFather.

N ")

}

}

ClassSonextendsFather

{

Protected$salutation= "Hey!"; / / the protected$salutation in the parent class is overwritten

Protectedidentify () in the protectedfunctionidentify () / / parent class is overridden

{

Print ("IamSon.

N ")

}

}

$obj=newSon ()

$obj- > getSalutation (); / / output Heyweight IamSon.

? >

/ Note: getSalutation () is not overridden in the subclass, but there is actually a getSalutation (). $salutation and identify () in this class

/ / dynamically bind to the getSalutation () method in the instance of the Son subclass, so call the getSalutation () method of the instance of Son

/ / the members salutation and identify () in the Son class will be called instead of the members salutation and identify () in the parent class.

Private members exist only within the class in which they reside. Unlike public and protected members, PHP simulates static binding. Look at example 6.11. Although the subclass overrides the value of salutation, the script binds this- > salutation with the current class Father. A similar principle applies to the private method identify ().

Listing6.11Bindingandprivatemembers

ClassFather

{

Private$salutation= "Hellothere!"

PublicfunctiongetSalutation ()

{

Print ("$this- > salutationn")

$this- > identify ()

}

Privatefunctionidentify ()

{

Print ("IamFather.

N ")

}

}

ClassSonextendsFather

{

Private$salutation= "Hey!"

Privatefunctionidentify ()

{

Print ("IamSon.

N ")

}

}

$obj=newSon ()

$obj- > getSalutation (); / / output Hellotherethereal Iambi.

? >

The advantage of dynamic binding is that it allows inheriting classes to change the behavior of the parent class, while maintaining the interface and functionality of the parent class, as shown in example 6.12. Because of the use of dynamic binding, the version of the isAuthorized invoked in deleteUser can be determined by the type of object. If it is a normal user,PHP call to User::isAuthorized, it will return FALSE. If it is an instance of AuthorizedUser, PHP calls AuthorizedUser::isAuthorized, which will allow deleteUser to execute smoothly.

/ / haohappy Note: to make it clear in one sentence, object types are bound to methods and properties. When calling a method that exists in both a parent class and a child class or accessing a property, it will first determine which object type the instance belongs to, and then call the methods and properties in the corresponding class.

Benefits of Listing6.12 dynamic binding

ClassUser// user

{

ProtectedfunctionisAuthorized () / / whether it is an authenticated user

{

Return (FALSE)

}

PublicfunctiongetName () / / get the name

{

Return ($this- > name)

}

PublicfunctiondeleteUser ($username) / / Delete user

{

If (! $this- > isAuthorized ())

{

Print ("Youarenotauthorized.

N ")

Return (FALSE)

}

/ / deletetheuser

Print ("Userdeleted.

N ")

}

}

ClassAuthorizedUserextendsUser// authenticated user

{

ProtectedfunctionisAuthorized () / / overwrite isAuthorized ()

{

Return (TRUE)

}

}

$user=newUser

$admin=newAuthorizedUser

/ / notauthorized

$user- > deleteUser ("Zeev")

/ / authorized

$admin- > deleteUser ("Zeev")

? >

Why the class members of private simulate static binding

To answer this question, you need to recall why private members are needed. When does it make sense to replace protected members with them?

Private members are used only if you don't want subclasses to inherit or specialize the behavior of their parents, which is less common than you think. In general, a good object hierarchy should allow most functional subclasses to specialize, improve, or change-this is one of the foundations of object-oriented programming. Private methods or variables are required in certain cases, for example, when you are sure that you do not want to allow the subclass to change a particular part of the parent class.

This is how PHP5.0 binds dynamically and why class members of private simulate static binding. The editor believes that there are some knowledge points that we may see or use in our daily work. I hope you can learn more from this article. For more details, please follow the industry information channel.

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