Is PHP Function Naming Case-Sensitive?

PHP Function Case Sensitivity

Regarding case sensitivity in PHP, it's important to understand the distinction between PHP language syntax (keywords, data types, etc.) and user-defined identifiers (functions, variables, classes).

Language Syntax

PHP language syntax is case-insensitive. This means that keywords, function and variable names, and data type names are not case-sensitive. For example, the following code snippet demonstrates that the "echo" keyword is treated the same whether it's written in lowercase or uppercase:

<code class="php">echo 'Hello, world!';  // Same as echo 'Hello, world!'.</code>

User-Defined Identifiers

Prior to PHP 5.0, user-defined identifiers (functions, variables, classes) were also case-insensitive. However, with the introduction of PHP 5.0, the behavior changed.

Function Names

As highlighted in the quote provided, PHP function names are case-insensitive. This means that you can call a function using different casing, and it will still be recognized. For example:

<code class="php">function myFunction() {}

myFunction();  // Same as MyFunction() or mYFUNCTION().</code>

User-Defined Constants

However, it's worth noting that user-defined constants are case-sensitive starting with PHP 5.0. This means that constants must be accessed using the exact case used in their definition.

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