Detailed explanation of anonymous functions and closure examples in php

1: Anonymous function

The anonymous function in php, also called the closure function, 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(){　　　　.... };
   eg: 把匿名函数赋值给变量，通过变量来调用
$closureFunc = function($str){　　 echo $str;  };  $closureFunc("hello world!");
  输出： hello world!

2: Closure

2.1 Put the anonymous function in a normal function, or you can return the anonymous function, which constitutes a Simple closure

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

2.2 Referring to local variables in anonymous functions

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

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, we need to quote a PHP keyword use. The code is as follows

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

2.3 Return to 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

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

2.5 How to use closures to change the variable values ​​​​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

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

2.6 Pass anonymous functions as parameters

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

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