5) PHP, variable variable

The so-called mutable variable is the name of a variable and a variable.

The syntax for mutable variables is a very special syntax for PHP--rare in other languages.

1 $v 1 = "abc";          // This is a string variable whose content is the string "abc" 2 3 ten;             // This is an ordinary variable whose content is the number ten 4 5 Echo  $ $v 1;          // at this point, it's called "mutable variables."

How to Understand:

1, when the $ symbol appears, it is possible to understand that it is a variable

2, here the first "$" appears, then PHP interprets it as a variable, the variable name is $V1;

3, we have to know that the value of $v 1 is "abc",

4, then, the name of the variable after the first "$" symbol is given as "ABC"

5, that is: Echo is trying to output a variable $abc, which is naturally the number 10

1 In fact, in theory, variable variables can be nested more, such as: $$ $def;   

5) PHP, variable variable