Subroutines – Behold the function

In this episode, let’s focus on functions within PHP. PHP lets you define a user-defined function, which is a subroutine. You define it using the keyword function. Then you give it a unique name. You can specify any parameters which are variables. These parameters allow your function to receive information to do work on when it’s called. Then you use the curly braces to block off the code that belongs to the function. That code does not run until the function is called.

Let’s look at the WordPress Core function called get_theme_mod(). We’ll look at the twentyseventeen theme and how it calls this function. We’ll talk about the syntax as well as option parameters and how they are used.

Then you’ll write a function to see how it works with and without parameters. You’ll also set a parameter as optional and see how it works.

Challenge Yourself

Can you start a function name with a $ sign?

No. The dollar sign $ is reserved for variables, as that’s how PHP knows it’s a variable and not a function or other construct.

You name functions the same way that you name variables except leave off the dollar sign.

How do you specify a function parameter as optional?

Optional parameters have an a default value assigned to them. If no value is passed to it, then the default value is used. For example, here is the optional parameter for get_theme_mod():

[php firstline=”855″]function get_theme_mod( $name, $default = false ) {
// … code left out for brevity
}[/php]

Notice how the parameter $default as an assignment operator, i.e. the equal sign, and a value, i.e. false.

True or False. When PHP loads a file, the code in a function runs immediately.

False. A function does not run until it’s called.

How do you call a function to use it in your code?

You specify it by the function’s name and then put parentheses after it. If there are required parameters, you have to specify those too.

Your code needs to go get a theme modification function that is called 'nav_menu_locations'. How would you do it?

You would use get_theme_mod and then pass it the name ‘nav_menu_locations’, like this:

[php]$menu_locations = get_theme_mod( ‘nav_menu_locations’ );[/php]