Detailed explanation of PHP anonymous functions and precautions_php skills

PHP5.3 not only introduces anonymous functions but also has many better new features. Let’s take a look at PHP anonymous functions and precautions. The specific content is as follows

Pre-PHP5.2: autoload, PDO and MySQLi, type constraints
PHP5.2: JSON support
PHP5.3: Deprecated features, anonymous functions, new magic methods, namespaces, late static binding, Heredoc and Nowdoc, const, ternary operator, Phar
PHP5.4: Short Open Tag, array abbreviation, Traits, built-in Web server, details modified
PHP5.5: yield, list() is used for foreach, details modified
PHP5.6: Constant enhancement, variable function parameters, namespace enhancement

Nowadays, most people use PHP5.3 and later versions, but I feel that a common phenomenon is that many new features have not been fully popularized after such a long time, and are rarely used in projects.

Look at PHP anonymous functions:

'test' => function(){
  return 'test'
},

The definition of PHP anonymous function is very simple, it is to assign a value to a variable, but this value is a function.

The above is to use the Yii framework to configure the components file and add a test configuration.

What are PHP anonymous functions?

See the official explanation:

Anonymous functions, are also called closures, allowing to temporarily create a function without a specified name. The value most commonly used as a callback function argument. Of course, there are other applications as well.

Anonymous function example

<&#63;php
echo preg_replace_callback('~-([a-z])~', function ($match) {
 return strtoupper($match[1]);
}, 'hello-world');
// 输出 helloWorld
&#63;>

Closure functions can also be used as the value of variables. PHP will automatically convert this expression into an object instance of the built-in class Closure. The method of assigning a closure object to a variable is the same as the syntax of ordinary variable assignment, and a semicolon is also added at the end:

Anonymous function variable assignment example

<&#63;php
$greet = function($name)
{
 printf("Hello %s\r\n", $name);
};
$greet('World');
$greet('PHP');
&#63;>

Closures can inherit variables from the parent scope. Any such variables should be passed in using the use language construct.

Inherit variables from parent scope

<&#63;php
$message = 'hello'
// 没有 "use"
$example = function () {
 var_dump($message);
};
echo $example();
// 继承 $message
$example = function () use($message) {
 var_dump($message);
};
echo $example();
// Inherited variable's value is from when the function
// is defined, not when called
$message = 'world'echo $example();
// Reset message
$message = 'hello'
// Inherit by-reference
$example = function () use(&$message) {
 var_dump($message);
};
echo $example();
// The changed value in the parent scope
// is reflected inside the function call
$message = 'world'echo $example();
// Closures can also accept regular arguments
$example = function ($arg) use($message) {
 var_dump($arg . ' ' . $message);
};
$example("hello");
&#63;>
 

Notes on anonymous functions in php

After php5.3, php added the use of anonymous functions. Today, an error occurred when using anonymous functions. You cannot declare and use them like php functions. See the code for details

$callback=function(){ 
 return "aa"; 
}; 
echo $callback(); 

It prints out as aa;

Look at the example below:

echo $callback(); 
$callback=function(){ 
 return "aa"; 
}; 

An error was reported at this time! $callback is undeclared, but no error will be reported when using functions declared by PHP itself!

function callback(){ 
 return "aa"; 
} 
echo callback(); //aa 
 
echo callback(); //aa 
function callback(){ 
 return "aa"; 
} 

Print both of these aa;

When using anonymous functions, the anonymous functions are used as variables and must be declared in advance. This is also the case in js! ! ! ! !

The above is the PHP anonymous functions and precautions introduced to you. I hope it will be helpful to your study.