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This article mainly introduces the php double $sign use case analysis of the relevant knowledge, the content is detailed and easy to understand, the operation is simple and fast, has a certain reference value, I believe you will have something to gain after reading this php double $symbol use case analysis article, let's take a look.

Double $symbol refers to "variable variable", is a unique variable in PHP, that is, a variable takes the value of another variable as its name, and the syntax "$$variable name"; variable variables can be used to dynamically set and use the variable name of a variable.

Operating environment of this tutorial: windows7 system, PHP7.1 version, DELL G3 computer

The double $symbol refers to a "variable", a unique variable in PHP that allows the name of a variable to be changed dynamically.

A variable is a variable that takes the value of another variable as its name.

A mutable variable gets the value of a normal variable as the variable name of the variable. Using this feature, we can dynamically set and use the variable name of a variable.

For example, we can set the value of $str:

$name = 'str'

So, we can use

Name replaces $str.

Name = 5

This code is equivalent to:

$str= 5

The use of variable variables

You only need to add at least two "$" symbols before the variable name.

Arrays use variable variables

In order to use the variable name of an array, you need to solve an ambiguity problem. That is, if you write $a [1], the parser needs to know whether you mean to use $a [1] as a variable or $an as a variable, and [1] refers to the index of the variable. The syntax to resolve this ambiguity is ${$a [1]} in the first case and ${$a} [1] in the second case.

Class properties can also be accessed through a variable property name. The variable attribute name is obtained from the access scope of the variable in which the call was made. For example, if your expression looks like this: $foo- > $bar, then the runtime will look for the variable $bar in the scope of the local variable, whose value will be used as a property name of the $foo object. You can also use $bar if it is an array.

Variable names cannot be used on super global array variables in PHP functions and classes. The variable $this is also a special variable that cannot be named dynamically.

Example

The following example uses a variable variable to change the name of a variable. The code is as follows:

Detailed explanation of examples:

First define two variables $str and $trans, and output the value of the variable $str, then use the variable to change the name of the variable $str, and finally output the value of the variable after the name has been changed

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