PHP Functions

Functions in PHP

Functions are the heart of functional programming. Functions are relationships between inputs and outputs. The arity of a function is the number of arguments a function accepts, and the function signature specifies return types and argument types. Lastly, the definition of a function encapsulates the function logic. Here’s a mathematically defined function:

$$f(x) = x + 1$$

It has an arity of one, and it increments the value of the parameter $x$ by 1. The parameter $x$ is effectively a placeholder for a general transformation given in the function definition using the addition operation: $x + 1$. Different results are obtained for different values of $x$ because the function offers localized computation. Each result is, therefore, unique to each input. For example:

$$f(2) = 3$$

$$f(3) = 4$$

Functions in PHP take on many forms. They’re just as flexible as variables and have the following characteristics:

• The function keyword.

• Two sets of parentheses:

  • Round brackets () for the arguments.
  • Curly braces {} for the function definition.

• A return type (as of PHP version 7.0).

Types of functions in PHP

The different types of functions in PHP are the following:

• Named functions
• Anonymous functions
• Closures
• Methods

Named functions

Named functions in PHP, like the one below, are identical (apart from a few syntactic differences) to those defined in other programming languages. They typically have an arbitrary name sandwiched between a function keyword and an argument list followed by the function definition, that contains state transformation expressions.