Creating shortcode question

[AlexKravchenko]

Hi everyone!

I am reading Brad Williams’ Professional WordPress Designer and Development book.

add_shortcode('hs', 'halloween_store_shortcode');
function halloween_store_shortcode ($atts, $content=null)
{
    //setting defaults
    extract(shortcode_atts(array('show'=>'')));
}

Eventually, within the content we insert a shortcode, such as this one: [hs show=price].

I am having hard time with understanding what shortcode_atts and extract functions do, although I have read their definitions in Codex and PHP.net

1. shortcode_atts:
   Combine user attributes with known attributes and fill in defaults when needed.

Questions:

• what are user attributes? Does it refer to attributes that are sent from shortcode macros, e.g. [hs show=price]?
• What are ‘known attributes’ since I did not define any attributes prior to this code?
• “combine”? how does it combine them? Into any array?

I appreciate your help. I could simply memorize it, but I don’t think that memorizing it will help me become good at WordPress.

and extract()
Import variables from an array into the current symbol table.

I assume shortcode_atts returns an array. “imports variables into current SYMBOL TABLE”?

What is a symbol table?

I appreciate any help with helping me understand that piece of code. Below is a full function definition to give you some context:

function halloween_store_shortcode($atts, $content = null)
{
    global $post;
    //it is like setting the defaults
    extract(shortcode_atts(array(
    "show" => '' //sets attribute default
    ), $atts ));
    
    //load options array
    $hween_options_arr = get_option('halloween_options');
    //load product data
    $hween_product_data = get_post_meta($post->ID,'_halloween_product_data', true);
    
    if ($show == 'sku')
    {
        $hs_show = !empty($hween_product_data['sku']) ? $hween_product_data['sku'] : '';
    }
    elseif ($show == 'price')
    {
        $hs_show = $hween_options_arr['currency_sign'];
        $hs_show = !empty($hween_product_data['price']) ? $hs_show . $hween_product_data['price'] : '';
    }
    elseif ($show == 'weight')
    {
        $hs_show = !empty($hween_product_data['weight']) ? $hween_product_data['weight'] : '';
    }    
    elseif ($show == 'color')
    {
        $hs_show = !empty($hween_product_data['color']) ? $hween_product_data['color'] : '';
    }
    elseif ($show == 'inventory' && !empty($hween_options_arr['show_inventory']))
    {
        $hs_show = !empty($hween_product_data['inventory']) ? $hween_product_data['inventory'] : '';
    }
    //return the shortcode value to display
    return $hs_show;
}

[megazoid]

@AlexKravchenko

and extract()Import variables from an array into the current symbol table.
I assume shortcode_atts returns an array. “imports variables into current SYMBOL TABLE”?
What is a symbol table?

extract does very simple thing, it creates separated variables from array items. Key of each item becomes variable name and value of item turns into value of that variable.

$array = ['name' => 'John', 'age' => 32];
extract($array);
echo $name; //John
echo $age; //32