What is a Callable?

Simply put, a callable is a part of your code that you can "call". When we say that you can "call" something, we mean that you can tell the program to execute it.

A callable can be written with parentheses after it, for example, functionName().

As previously described, a function is a type of callable, so a function can be called (that is, you can tell your program to execute it).

As an example, consider the following user-defined function:

function howManyTimesDidWeTellYou(int $numberOfTimes): string
{
    return "You told me $numberOfTimes times";
}

Do not worry about the details of the function right now—we will get into the nitty-gritty of it later. This function could be defined anywhere in your code, but let's assume that it is defined in a script called how-many-times-did-we-tell-you.php.

The contents of the script would then look like this:

<?php
declare(strict_types=1...