Understand PHP anonymous functions in five minutes (detailed examples)

In the previous article, I brought you "How to use PHP callback functions (detailed examples)". This article introduces the relevant knowledge of callback functions in PHP in detail. This article Let’s take a look at the basic anonymous functions in PHP functions and what are the knowledge points worth paying attention to. Hope it helps everyone!

PHP Anonymous Function

What is an anonymous function?

Anonymous functions are also called closure functions.

What is a closure? A closure is a code block that can have free variables; these variables are not defined within this code or elsewhere globally, but are defined in the environment in which the code block is defined, that is, local variables. The word "closure" comes from the combination of a block of code to be executed and a computational environment that provides bindings for free variables. Because free variables are contained within a code block, these free variables and the objects they refer to are not released. In fact, we can put it in layman's terms: child functions can use local variables in the parent function. This behavior is called closure. Theoretically, closures and anonymous functions are different concepts, but PHP treats them as the same concept. When it comes to closures, it means anonymous functions, and when it comes to anonymous functions, it means closures.

That is to say, a function without a function name. PHP can create a function without a name, and anonymous functions are mostly used in callback functions.

Anonymous functions can directly assign the assigned value to the variable. The anonymous function is still a function. You can pass in parameters and directly assign the assigned value to the variable. Calling the variable is called the function.

The syntax structure of creating an anonymous variable is as follows:

function (参数列表) {
    ...
}

Anonymous functions are very similar to ordinary functions. They can have return values ​​and can also accept parameters. The difference is that anonymous functions will Omit the function name when declaring it.

The example is as follows:

<?php
    $a = function (){
        return &#39;好好学习，天天向上&#39;;
    };
    echo $a();
?>

Output result:

As can be seen from the above example, the anonymous function is used as The value of the variable is used. At this time, PHP will automatically convert this expression into a built-in class expression. The method of assigning a closure to a variable is the same as the ordinary variable assignment syntax. At the end, " ;"(semicolon).

Next, let’s look at two combined anonymous functions

• Variable functional anonymous function

<?php
$a = function($b)
{
 echo $b.&#39;好好学习&#39;;
};
$a(&#39;福如东海&#39;);
$a(&#39;寿比南山&#39;);
?>

Output result:

The function body in the above example has no function name and is called by $a plus parentheses. This is the variable functional formula Anonymous function.

• Callback-style anonymous function

#In our actual use, anonymous functions are often regarded as functions or The use of method callbacks, not only callback functions, but also anonymous functions are used in many PHP functions. The sample code is as follows:

<?php
    $a   = [1,2,3,4,5,6];
    $b = array_map(function ($c) {
        return $c*$c;
    }, $a);
    echo &#39;<pre class="brush:php;toolbar:false">&#39;;
    print_r($b);
?>

Output result:

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