具有已知参数的数组

Question

I've not that new to php but am trying to figure out how exactly this piece of code reads.

$actions = array();  

function add_action( $hook, $function )  
{  
    global $actions;  

    // create an array of function handlers if it doesn't already exist  
    if( !isset( $actions[ $hook ] ) )  
        $actions[ $hook ] = array();  

    // append the current function to the list of function handlers  
    $actions[ $hook ][] = $function;  
}  

here is my understanding but I believe I'm completely wrong - variable actions is given an array with no params, then a function is created and actions is made into a global giving it global scope. Then there a condition the bit I don't understand that somehow checks for a parem. $actions[ $hook ] its what this bit means that confuses me. is it calling into the array? and why are blank arrays set to variables?

Thanks for clearing this up for me

Answer 1

First we are declaring a php variable $actions within the global scope:

$actions = array();

Then in the function, you use the global keyword to declare that you are using an already defined global value instead of creating a new value within the scope of the function:

global $actions;

Next, it is using the isset() function to check if the value $hook exists as an index of our global $actions. If the index does not exist, it creates that index and assigns it an empty array as the value.

// create an array of function handlers if it doesn't already exist  
if( !isset( $actions[ $hook ] ) )  
    $actions[ $hook ] = array();

Last, it is using the bracket operator on the array it was just given to append a new value to it, in this case it is giving it the value of $function.

// append the current function to the list of function handlers  
$actions[ $hook ][] = $function;  

So in the end, you have the global $actions variable with an index of $hook which has an array value, and that array value has an index added to it with the value of $function.