Certainly! Let’s delve into the technical distinctions between constants and variables in PHP with the aid of reliable sources.
In PHP, a variable is a symbol or name that holds a value that can change or be reassigned throughout the execution of the script. Variables in PHP are represented by a `$` sign followed by the name of the variable, for instance, `$variableName`. You can assign any value to a variable, including integers, strings, arrays, or objects, and these values can be modified after their initial assignment. Here is an example of a variable in PHP:
```
$greeting = “Hello, World!”;
echo $greeting; // Output: Hello, World!
$greeting = “Hello, PHP!”;
echo $greeting; // Output: Hello, PHP!
?>
```
In this case, the `$greeting` variable initially holds the value “Hello, World!” which is then changed to “Hello, PHP!”.
A constant, on the other hand, is an identifier or a simple name that holds a value which cannot be changed during the execution of the script. Constants are defined using the `define()` function or the `const` keyword within classes. Unlike variables, constants are not prefixed with a `$` sign. They are conventionally named using uppercase letters. Here is an example of defining and using a constant in PHP:
```
define(“GREETING”, “Hello, World!”);
echo GREETING; // Output: Hello, World!
const FAREWELL = “Goodbye, World!”;
echo FAREWELL; // Output: Goodbye, World!
?>
```
In the example above, `GREETING` and `FAREWELL` are constants and their values cannot be altered once set.
Key Differences:
1. Syntax:
- Variables: Prefixed with the `$` symbol (e.g., `$variableName`).
- Constants: Defined using `define(‘NAME’, ‘value’)` or `const NAME = ‘value’` without a `$` prefix.
1. Mutability:
- Variables: Their values can be changed after they are initially set.
- Constants: Their values are immutable post-initialization.
1. Scope:
- Variables: Global or local scope depending on where they are defined.
- Constants: Global by default and can be accessed anywhere in the script after they are defined. Constants within classes (defined using `const`) have a class scope.
1. Use Case:
- Variables are used when you want to store data that may change during script execution.
- Constants are used for values that should not change after they have been set (e.g., configuration settings, fixed data values).
According to the [PHP Manual](https://www.php.net/manual/en/language.constants.php), constants are case-sensitive by default; however, with `define()`, you can create case-insensitive constants by passing `true` as the third argument. For instance:
```
define(“GREETING”, “Hello, World!”, true);
echo GREETING; // Output: Hello, World!
echo greeting; // Output: Hello, World! (case-insensitive)
```
To sum up, variables and constants serve different purposes and follow different rules within PHP scripts. Variables are dynamic and mutable, suitable for data that may change, whereas constants are static and immutable, holding data that remains constant throughout the script. These distinctions are foundational to understanding and effectively using PHP for web development and other scripting tasks.
Sources Used:
1. PHP Manual – Constants: https://www.php.net/manual/en/language.constants.php
2. PHP Manual – Variables: https://www.php.net/manual/en/language.variables.php
