PHP's variable variable application _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:

2. $a = ' Hello ';
3. ?>

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.

2. $ $a = ' world ';
3. ?>

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:

2. echo "$a ${$a}";
3. ?>

Exactly the same as the output of the following statement:

2. echo "$a $hello";
3. ?>

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 $bar. "n"; Echo $foo-$baz [1]. "N";? > The above example will output the following result: 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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