Useful Wordpress code

usefulwordpress.php

<?php
//==================================
// ONLY ONE ITEM IN THE CART AT TIME
//==================================
add_filter( 'woocommerce_add_cart_item_data', 'woo_custom_add_to_cart' );
function woo_custom_add_to_cart( $cart_item_data ) {
    global $woocommerce;

    // REMOVE ALL OTHER ITEMS
    $woocommerce->cart->empty_cart();

    //RETURN JUST THE NEW ONE...
    return $cart_item_data;
}

//==================================
// SHORTCODE CREATION
//==================================
// usage - [shortcodename] will display <h1>SHORTCODE HTML RETURN</h1>
add_shortcode('shortcodename', 'shortcode_function');

function shortcode_function($attrs){
    //if you want to handle the attributes, it will be an item in the array
    // ie. [shortcodename title="Title H1"] will populate the $attrs var
    // $attrs["title"]
    return "<h1>SHORTCODE HTML RETURN</h1>";
}