Detailed explanation of using PHP closure (Closure)_PHP tutorial

I unknowingly discovered that PHP has been released to version 5.5, and I have been using PHP5.2, which makes me look like a young man from the mountains, rustic and backward. After I got used to using closures in JavaScript, I suddenly became interested in PHP's closures.

So I downloaded a WAMP integrated development environment online, which is the PHP5.3 version (PHP5.3 began to introduce the closure feature). I have to say that WAMP is really convenient to install and use. After a simple configuration, let's get started.

Anonymous function
When you mention closures, you have to think of anonymous functions, also called closure functions (closures). It seems that PHP closure implementation mainly relies on it. Declaring an anonymous function is like this:

Copy code The code is as follows:

$func = function() {

}; //With the terminator

You can see that because the anonymous function has no name, if you want to use it, you need to return it to a variable. Anonymous functions can also declare parameters like ordinary functions, and the calling method is also the same:

Copy code The code is as follows:

$func = function( $param ) {
echo $param;
};

$func( 'some string' );

//Output:
//some string

By the way, before PHP introduced closures, there was also a function that could create anonymous functions: create function, but the code logic was only It can be written as a string, which looks obscure and difficult to maintain, so few people use it.

Implement closures
Pass anonymous functions as parameters in ordinary functions, and they can also be returned. This implements a simple closure.

There are three examples below

Copy the code The code is as follows:

//Example 1
//Define an anonymous function in the function and call it
function printStr() {
$func = function( $str ) {
echo $str;
};
$func( 'some string' );
}

printStr();

//Example 2
//Return the anonymous function in the function and call it
function getPrintStrFunc() {
$func = function( $str ) {
echo $str;
};
return $func;
}

$printStrFunc = getPrintStrFunc();
$printStrFunc( 'some string' );

//Example 3
//Pass the anonymous function as a parameter and call it
function callFunc( $func ) {
$func( 'some string' );
}

$printStrFunc = function( $str ) {
echo $str;
};
callFunc( $printStrFunc );

//You can also pass anonymous functions directly. If you know js, this writing method may be familiar
callFunc( function( $str ) {
echo $str;
} );

Connect the closure to the outside world Keywords for variables: USE
Closures can save some variables and values ​​​​in the context of the code block. By default in PHP, anonymous functions cannot call context variables in the code block where they are located, but need to use the use keyword.

Let’s take a look at another example:

Copy the code The code is as follows:

function getMoney() {
$ rmb = 1;
$dollar = 6;
$func = function() use ( $rmb ) {
echo $rmb;
echo $dollar;
};
$ func();
}

getMoney();

//Output:
//1
//Error, dollar variable not found

As you can see, dollar is not declared in the use keyword, in this anonymous It cannot be obtained in the function, so attention should be paid to this issue during development.

Some people may wonder whether it is possible to change the context variables in an anonymous function, but I found that it is not possible:

Copy the code The code is as follows:

function getMoney() {
$rmb = 1;
$func = function() use ( $rmb ) {
echo $rmb;
// Add 1 to the value of $rmb
$rmb++;
};
$func();
echo $rmb;
}

getMoney();

//Output:
//1
//1

Ah, it turns out that what use refers to is just a copy of the variable. But I want a full reference to the variable, not a copy.

To achieve this effect, just add an & symbol before the variable:

Copy the code The code is as follows:

function getMoney() {
$rmb = 1;
$func = function() use ( &$rmb ) {
echo $rmb;
//Add the value of $rmb 1
$rmb++;
};
$func();
echo $rmb;
}

getMoney();

//Output:
//1
//2

Okay, so the anonymous function can reference the context variables. If the anonymous function is returned to the outside world, the anonymous function will save the variables referenced by use, but the outside world will not be able to obtain these variables. In this way, the concept of 'closure' may be clearer.

Change the above example according to the description:

Copy the code The code is as follows:

function getMoneyFunc() {
$rmb = 1;
$func = function() use ( &$rmb ) {
echo $rmb;
//Add 1 to the value of $rmb
$rmb++;
};
return $func;
}

$getMoney = getMoneyFunc();
$getMoney();
$getMoney();
$getMoney();

//Output:
//1
//2
//3

Summary
The characteristics of PHP closures are not too surprising. Practical CLASS can achieve similar or even more powerful functions, and it cannot be compared with js closures. We can only look forward to improvements in PHP's closure support in the future. However, anonymous functions are still quite useful. For example, when using functions such as preg_replace_callback, you don't need to declare a callback function externally.

http://www.bkjia.com/PHPjc/326881.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/326881.htmlTechArticleI unknowingly discovered that PHP has been released to version 5.5, and I have been using PHP5.2, which makes me look Like the young man who came from the mountains, he is rustic and backward. I am used to using closures in javascript...