PHP implements a method of code reuse, called trait

Since PHP 5.4.0, PHP has implemented a code reuse method called trait.

Trait is a code reuse mechanism that is prepared for PHP-like single-inheritance languages. Trait to reduce the limitations of single-inheritance languages, developers are free to reuse method in separate classes within different hierarchies.

Trait is a solution for PHP multiple inheritance. For example, it would be cumbersome to inherit two Abstract classes at the same time, Trait to solve the problem.

It adds a combination of horizontal features to traditional inheritance.

Example 1: Defining trait with the trait keyword

Trait first_trait{public    function Hello () {        return ' hello ';    }}

Example 2: Using Trait in class, using the Use keyword, separated by commas when using multiple trait

Trait first_trait{public    function Hello () {        return ' hello ';    }} Trait second_trait{public    function World () {        return ' world ';    }} Class first_class{use    first_trait,second_trait;} $obj =new First_class (); Echo $obj->hello (); Echo $obj->world ();

Example 3: Priority

Members that inherit from the base class are overwritten by the members that are inserted by trait. Precedence is the method from which the member of the current class overrides the trait, and trait overrides the inherited method.

Example: A member inherited from a base class is overwritten by a member inserted by trait

Class Base {public    function SayHello () {        echo ' Hello ';    }} Trait Sayworld {public    function SayHello () {        Parent::sayhello ();        Echo ' world! ';    }} Class Myhelloworld extends Base {use    Sayworld;} $o = new Myhelloworld (); $o->sayhello ();//result of output Hello world!

Example: the member of the current class overrides the Trait method

Trait HelloWorld {public    function SayHello () {        echo ' Hello world! ';    }} Class Theworldisnotenough {use    HelloWorld;    Public Function SayHello () {        echo ' Hello universe! ';    }} $o = new Theworldisnotenough (); $o->sayhello ();//result of output Hello universe!

Example of nesting between 4:trait

Trait first_trait{public    function Hello () {        echo ' hello ';    }} Trait second_trait{    //trait between the nested use    first_trait;    Public Function World () {        echo ' world ';    }} Class first_class{use    second_trait;} $obj =new First_class (); Echo $obj->hello (); Echo $obj->world ();

Example 5: You can declare an abstract method in trait, use its class or trait to implement an abstract method

Trait first_trait{public    function Hello () {        echo ' hello ';    }    Abstract method public abstract    function test ();} Trait second_trait{    //trait between the nested use    first_trait;    Public Function World () {        echo ' world ';    }    Implement the test method in first_trait public    function test () {        echo '! ';    }} Class first_class{use    second_trait;} $obj =new First_class (); Echo $obj->hello (); Echo $obj->world (); Echo $obj->test ();//Output helloworld!

Example 6: conflict resolution

If two trait all insert a method with the same name, a fatal error will occur if the conflict is not resolved explicitly.

In order to resolve the naming conflicts of multiple trait in the same class, it is necessary to use the insteadof operator to explicitly specify which of the conflicting methods to use.

The above method only allows other methods to be excluded, as operator can introduce one of the conflicting methods to another name, equivalent to the alias of the method.

Trait A {public    function SmallTalk () {        echo ' A ';    }    Public Function Bigtalk () {        echo ' A ';    }} Trait B {public    function SmallTalk () {        echo ' B ';    }    Public Function Bigtalk () {        echo ' B ';    }} Class Talker {Use    A, b {        b::smalltalk insteadof A;//trait B's SmallTalk method will replace the trait method of SmallTalk A A::bigta        LK Insteadof B;  The Bigtalk method of trait a replaces the Bigtalk method of trait B    }}class aliased_talker {use    A, b {        b::smalltalk insteadof a;//t The Smalltalk method of the Rait B replaces the Smalltalk method of trait a A::bigtalk insteadof method of A is a b;//trait method        instead of Bigtalk b        : : Bigtalk as Talk; Use the AS operator to define the talk method as the alias of the Bigtalk method of B    }} $obj =new Talker (), $obj->smalltalk (), $obj->bigtalk ();//Results Output BA $obj 2=new Aliased_talker (); $obj 2->talk ();//outputs B

Example 7: Modify access control for a method

Trait HelloWorld {public    function SayHello () {        echo ' Hello world! ';    }} Modify SayHello access Control class MyClass1 {use    HelloWorld {SayHello as protected;}} Give method a changed access control alias//original SayHello access control is not changed class MyClass2 {use    HelloWorld {SayHello as Private Myprivatehello;}}

Example 8:trait can also define attributes

Trait propertiestrait {public    $x = 1;} Class Propertiesexample {use    propertiestrait;} $example = new Propertiesexample; $example->x;

If trait defines an attribute, the class will not be able to define a property of the same name, or an error will result. If the attribute's definition in the class is compatible with the definition in trait (the same visibility and initial value) then the error level is E_STRICT , otherwise it is a fatal error.

Trait propertiestrait {public    $same = true;    Public $different = false;} Class Propertiesexample {use    propertiestrait;    Public $same = true; Strict Standards Public    $different = true;//Fatal error}

PHP implements a method of code reuse, called trait