The usual variables are named by the following statements:
Copy CodeThe code is as follows:
$a = ' Hello ';
?>
A mutable variable name refers to the use of a variable's value as the name of the variable. In the example above, by using two $ symbols, you can set the hello to a variable name, as in the following.
Copy CodeThe code is as follows:
$ $a = ' world ';
?>
With the above two statements, two variables are defined: The variable $ A, the contents are "Hello" and the variable $hello, the content is "world". So, the following language:
Copy CodeThe code is as follows:
echo "$a ${$a}";
?>
Exactly the same as the output of the following statement:
Copy CodeThe code is as follows:
echo "$a $hello";
?>
They all output: Hello world.
In order to use the variable variable name of the array, you need to solve a 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 to use the $ $a as a variable, [1] to refer to the index of the variable. The syntax for solving this ambiguity is: The first case uses ${$a [1]}, and the second case uses ${$a}[1].
Class properties can also be accessed through variable property names. A mutable property name is obtained from the access scope of the variable where the call is generated. For example, if your expression is this: $foo-$bar, the runtime will look for the variable $bar within the scope of the local variable, and its value will be a property name for the $foo object. If the $bar is an array, it can be used.
Example 1 variable variable name
Copy CodeThe code is as follows:
class Foo {
var $bar = ' I am bar ';
}
$foo = new Foo ();
$bar = ' Bar ';
$baz = Array (' foo ', ' Bar ', ' baz ', ' Quux ');
$bar Echo $foo. "N";
$baz echo $foo [1]. "N";
?>
The above example will output the following results:
I am Bar.
I am Bar.
Warning
Note that mutable variable names cannot be used on PHP functions and super Global array variables in classes. Variable $this is also a special variable that cannot be named dynamically.
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