Functions and Closures

Since PHP 7, functions have gained typed parameters and returns, named arguments, arrow functions and closures you pass around as values, and in 8.5 closures inside constant expressions. Underneath, the value model is unchanged: arrays are copied lazily, objects travel as handles, and & makes a true alias. The section ends there, because most baffling PHP bugs start there.

Subsections

• Declaring Functions
• Type Declarations
• Named Arguments and Variadics
• Anonymous Functions
• Arrow Functions
• First-Class Callables
• Closures in Constants
• Calling Functions Dynamically
• Callbacks
• References and Scope