Detailed explanation of anonymous functions and closures in php-PHP Tutorial-php.cn

Detailed explanation of anonymous functions and closures in php

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Release： 2023-03-11 17:30:01

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1: Anonymous functions (can only be used in php5.3.0 or above)

Anonymous functions in php (Anonymous functions) , also called closure function (closures), allows you to specify a function without a name. The most commonly used one is the parameter value of the callback function

Definition of anonymous function:

$closureFunc = function(){

　　　　....

 };

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eg: Assign the anonymous function to the variable, through the variable To call

 $closureFunc = function($str){

　　 echo $str;

  };  $closureFunc("hello world!");

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Output: hello world!

2: Closure

2.1 Place the anonymous function in the ordinary function , you can also return the anonymous function, which constitutes a simple closure

function closureFunc1(){
    $func = function(){
        echo "hello";
    };
    $func();
}
closureFunc1();
//输出: hello

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2.2 In the anonymous function Reference local variable

function closureFunc2(){
    $num = 1;
    $func = function(){
        echo $num;
    };
    $func();
}
closureFunc2();
//Notice: Undefined variable: num

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After the above function is run, a Notice error will be reported, indicating that we cannot use local variables in anonymous functions. At this time, a PHP keyword use must be quoted. The code is as follows

function closureFunc2(){
    $num = 1;
    $func = function() use($num){
        echo $num;
    };
    $func();
}
closureFunc2();
//输出: 1

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2.3 Return anonymous function

function closureFunc3(){
    $num = 1;
    $func = function() use($num){
        echo $num;
    };
    return $func;
}
$func = closureFunc3(); //函数返回匿名函数
$func(); //然后我们在用$func() 调用
//输出: 1

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2.4 How do we pass parameters to the anonymous function when we return it? In fact, it is the same as passing parameters to a normal function.

function closureFunc4(){
    $num = 1;
    $func = function($str) use($num){
        echo $num;
        echo "\n";
        echo $str;
    };
    return $func;
}
$func = closureFunc4();
$func("hello, closure4");
//输出:
//1
//hello, closure4

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2.5 How to use closure to change the variable value referenced by the context?

function closureFunc5(){
    $num = 1;
    $func = function() use($num) {
        echo "\n";
        $num++;
        echo $num;
    };
    echo "\n";
    echo $num;
    return $func;
}
$func = closureFunc5();
$func();
$func();
$func();
//输出:
// 1
// 2
// 2
// 2

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Looking at the above input results, it is obvious that the purpose has not been achieved. In fact, just add an & reference symbol.

function closureFunc5(){
    $num = 2;
    $func = function() use(&$num) {
        echo "\n";
        $num++;
        echo $num;
    };
    echo "\n";
    echo $num;
    return $func;
}
$func = closureFunc5();
$func();
$func();
$func();
//输出:
// 2
// 3
// 4
// 5

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2.6 Pass anonymous functions as parameters

function callFunc($func){
    $func("argv");
}

callFunc(function($str){
    echo $str;
})
//输出：
// argv

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