Introduction to the characteristics and usage of Trait in PHP (with code)

This article introduces to you the characteristics and usage of Trait in PHP (with code). It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

Since PHP5.4.0, PHP has implemented 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 includes the specific implementation (indicating its class characteristics)
Simple use
First of all, of course, declare a Trait, PHP5.4 added trait Keyword

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

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

class first_class {
// 注意这行，声明使用 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
in the same Class You can use multiple Traits

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
Trait 之间的嵌套
同时，Trait 之间也可以相互的嵌套，例如
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 the Trait, so that the Class that uses it must implement it

trait first_trait {
function first_method() { echo "method"; }
// 这里可以加入修饰符，说明调用类必须实现它
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 syntax perspective: insteadof and as. For usage, please refer to

trait first_trait {
function first_function() { 
echo "From First Trait";
}
}
trait second_trait {
// 这里的名称和 first_trait 一样，会有冲突
function first_function() { 
echo "From Second Trait";
}
}
class first_class {
use first_trait, second_trait {
// 在这里声明使用 first_trait 的 first_function 替换
// second_trait 中声明的
first_trait::first_function insteadof second_trait;
}
} 
$obj = new first_class();
// Output: From First Trait
$obj->first_function();

. The above are some basic uses of Trait. 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 , you can use multiple Traits
Trait supports modifiers, such as final, static, abstract
We can use insteadof and as operators to resolve conflicts between Traits

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