Sharing the characteristics and functions of Trait in PHP

Traits is a code reuse mechanism prepared for single inheritance languages ​​like PHP. Traits are designed to reduce the constraints of single-inheritance languages ​​and allow developers to freely reuse method sets in independent classes within different hierarchies.

Since PHP 5.4.0, PHP implements a method of code reuse called traits.

Traits is a code reuse mechanism prepared for single inheritance languages ​​like PHP. Traits are designed to reduce the constraints of single-inheritance languages ​​and allow developers to freely reuse method sets in independent classes within different hierarchies. The semantics of traits and class composition define a way to reduce complexity and avoid the typical problems associated with traditional multiple inheritance and mixins.

Trait is similar to a class, but is only designed to combine functionality in a fine-grained and consistent way. Trait cannot be instantiated by itself. It adds a combination of horizontal features to traditional inheritance; that is, members of application classes do not need to be inherited.

Trait was added in PHP5.4. It is neither an interface nor a class. Mainly to solve the limitations of single inheritance languages. It is a solution to multiple inheritance in PHP. For example, it would be very troublesome to inherit two Abstract Classes at the same time. Trait is designed to solve this problem. It can be added to one or more existing classes. It declares what the class can do (indicating its interface characteristics), and also contains the specific implementation (indicating its class characteristics)

Simple use

First, Of course, declare a trait. PHP5.4 adds the trait keyword

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trait first_trait { function first_method() { /* Code Here */ } function second_method() { /* Code Here */ } }

At the same time, if you want to use the Trait in Class, use the use keyword

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class first_class { // Note this line, declare the use of first_trait use first_trait; } $obj = new first_class(); // Executing the method from trait $obj->first_method(); // valid $obj->second_method(); // valid

Use multiple Traits

You can use multiple Traits in the same Class

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trait first_trait { function first_method() { echo "method"; } } trait second_trait { function second_method() { echo "method"; } } class first_class { // now using more than one trait use first_trait, second_trait; } $obj= new first_class(); // Valid $obj->first_method(); // Print : method // Valid $obj->second_method(); // Print : method

Nesting between Traits

At the same time, Traits can also be nested within each other, such as

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trait first_trait { function first_method() { echo "method"; } } trait second_trait { use first_trait; function second_method() { echo "method"; } } class first_class { // now using use second_trait; } $obj= new first_class(); // Valid $obj->first_method(); // Print : method // Valid $obj->second_method(); // Print : method

Abstract Method of Trait

We can declare the abstract method that needs to be implemented in Trait, so that the Class that uses it must implement it

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##trait first_trait { function first_method() { echo "method"; } // You can add modifiers here to indicate the call Classes must implement it abstract public function second_method(); } class first_method { use first_trait; function second_method() { /* Code Here */ } }

Trait conflict

Using multiple Traits at the same time will inevitably lead to conflicts, which we need to resolve. PHP5.4 brings related keyword syntax from the aspect of grammar: insteadof and as. For usage, see

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trait first_trait { function first_function() { echo "From First Trait"; } } ##trait second_trait { // The name here is the same as first_trait, there will be a conflict function first_function() { echo "From Second Trait"; } } class first_class { use first_trait, second_trait { //Declare here the replacement of first_function with first_trait // ##first_trait::first_function instead of second_trait; } ## declared in second_trait #} <p class="line number19 index18 alt2" style="line-height:15.4px;margin:0px;padding:0px 1em;background-image:none;border:0px;float:none;vertical-align:baseline;min-height:auto;white-space:pre;"><code class="php variable" style="margin:3px auto 0px;padding:0px 0px 0px 5px;background:rgb(255,255,255);border-left:3px solid rgb(108,226,108);font-size:14px;clear:both;border-top:0px;border-right:0px;border-bottom:0px;float:none;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(170,119,0);">$obj = new first_class(); // Output: From First Trait $obj->first_function();

The above are some basic uses of Traits. For more details, please refer to the official manual. Here are some points to note:

Trait will override the parent class method inherited by the calling class

Trait cannot be instantiated using new like Class

A single Trait can be composed of multiple Traits

In a single Class, multiple Traits can be used

Trait supports modifiers, For example, final, static, abstract

We can use insteadof and as operators to resolve conflicts between Traits

Related recommendations:

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Detailed explanation on the use of traits reuse mechanism in php

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