PHP variable variable name _php tutorial

Sometimes variable names can be a great convenience for programming. This means that variable names can be dynamically named and used. The usual variables are named by the following statements:

 
  
  

  
   
   
 Php
  
   
   
$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.

 
  
  

  
   
   
 Php
  
   
   
$$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:

 
  
  

  
   
   
 Php
  
   
   

  
   
   
?>
 
  
  

Exactly the same as the output of the following statement:

 
  
  

  
   
   
 Php
  
   
   

  
   
   
?>
 
  
  

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

 
 

  
  

  
 PHP  
  
  

  
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

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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