Understand the characteristics and functions of Traits in PHP

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 includes the specific implementation (indicating its class characteristics)

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Easy to use

First of all, of course, declare a Trait. PHP5.4 adds the trait keyword

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, 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

can be used in the same Class 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

Nesting between Traits

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

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

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, 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

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