What is a PHP Function?

A php function is an object-oriented programming method. It allows the logic of an application to be separated into smaller units of work, reducing code complexity and making it easier for developers to understand the overall flow of their applications. Functions can also be re-used across multiple applications, increasing efficiency and reducing the amount of duplicate code in a project.

In PHP, functions are defined using the keyword function followed by the name of the function and then the curly braces which contain the code that will be executed. A function can take one or more arguments which are passed to the function when it is called, allowing the function to perform its work. A return statement is used to return the final output of the function once it has finished.

When a variable is passed to a function, the variable can be passed by reference or by value. When a variable is passed by reference, a new entry is added to the PHP symbol table which references an internal data structure that contains the variables type and value. This means that the variable can be accessed within and outside of the function. This is known as variable scope.

When passing variables by value, the original value of the variable is retained. This is usually used when passing values that cannot be changed, such as an integer, to the function. If the function is changed, for example, to change an integer to a string, PHP will throw a fatal error because of the data type mismatch. PHP has support for strict data typing which is enabled by adding a colon and the intended data type to the end of the function definition, before the opening curly brace.