Sharing how to use variable variable names in PHP_PHP tutorial

Usually variables are named by the following statement:

Copy code The code is as follows:

$ a = 'hello';
?>

Variable variable name refers to using the value of a variable as the name of the variable. In the example above, you can set hello to the name of a variable by using two $ signs, like below.

Copy code The code is as follows:

$$a = 'world';
?>

Through the above two statements, two variables are defined: variable $a, which contains "hello" and variable $hello, which contains "world". So, the following language:

Copy code The code is as follows:

echo "$a $ {$a}";
?>

The output of the following statement is exactly the same:

Copy code The code is as follows:

echo "$a $hello";
?>

They all output: hello world.
In order to use mutable variable names for arrays, you need to resolve an ambiguity problem. That is, if you write $$a[1], the parser needs to understand whether you mean to treat $a[1] as a variable, or to treat $$a as a variable. [1] refers to this variable. index. The syntax to resolve this ambiguity is: use ${$a[1]} in the first case and ${$a}[1] in the second case.
Class properties can also be accessed via mutable property names. Mutable property names are taken from the access scope of the variable in which the call was made. For example, if your expression is like this: $foo->$bar, then the runtime will look for the variable $bar in the local variable scope, and its value will be used as a property name of the $foo object. It can also be used if $bar is an array.
Example 1 Variable variable name

Copy code The code is as follows:

class foo {
var $bar = 'I am bar.';
}
$foo = new foo();
$bar = 'bar';
$baz = array('foo ', 'bar', 'baz', 'quux');
echo $foo->$bar . "n";
echo $foo->$baz[1] . "n";
?>

The above example will output the following results:
I am bar.
I am bar.
Warning
Please note that, Variable variable names cannot be used for super global array variables in PHP functions and classes. The variable $this is also a special variable that cannot be dynamically named.

http://www.bkjia.com/PHPjc/325022.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/325022.htmlTechArticleUsually variables are named by the following statement: Copy the code The code is as follows: ?php $a = 'hello'; ? Variable variable name refers to using the value of a variable as the name of the variable. On...