In PHP, variables are fundamental to programming, serving as containers for storing data values. Here is a comprehensive overview:
Definition and Basics
- Variable Declaration: Variables in PHP start with the $ sign followed by the name of the variable. They are case-sensitive.
- Dynamic Typing: PHP supports dynamic typing, meaning a variable's type can change during the script's execution. This differs from static typing where variable types must be declared beforehand.
- Types: PHP variables can hold different types of data including:
- Scalars (integer, float, string, boolean)
- Compound (array, object)
- Special (resource, NULL)
Variable Scope
- Local Variables: Defined within a function, and not accessible outside of it.
- Global Variables: Accessible from anywhere in the script, declared using the 'global' keyword within functions.
- Static Variables: Retain their value between function calls.
History and Context
- Origin: PHP was created by Rasmus Lerdorf in 1994 initially as a set of Perl scripts to track his visitors. Variables in PHP evolved from these early scripts to become a key feature of the language.
- Development: With each version of PHP, variable handling has been refined. For example, PHP 4 introduced references, PHP 5 enhanced object-oriented programming capabilities affecting variable use, and PHP 7 brought performance improvements impacting how variables are processed.
Use Cases and Examples
- Simple Assignment:
$name = "John";
$age = 30;
- Variable Variables: A variable variable takes the value of a variable and treats that as the name of another variable.
$foo = "bar";
$$foo = "Hello"; // Now $bar equals "Hello"
- Variable References: PHP allows assigning references to variables with the =& operator.
$a = "Hello";
$b =& $a; // $b is now a reference to $a
Sources and Further Reading
Related Topics