wishlist.php

				<form method="POST" name="wishlist" >
					<input type="number" min="0" name="wl_quantity" value="1" />
					<input type="hidden" name="wl_product" value="<?php echo $post->ID; ?>" />
					<input type="submit" value="<?php printf( __( 'add product') ); ?>" />
				</form>

				<?php
					// If user is logged in and has capability 'read'
					if( current_user_can( 'read' ) ) {
						// Create the wishlist array
						$_SESSION[ 'wishlist' ] = array();
					}
					
					// Check if a request for adding product ID to wishlist was made
					if( isset( $_REQUEST[ 'wl_product' ] ) && intval( $_REQUEST[ 'wl_product' ] ) ) {						
						// Add the product ID to the wishlist
						$_SESSION[ 'wishlist' ][ 'product_id' ] = intval( $_REQUEST[ 'wl_product' ] );
					}
					
					// Check if a request for adding product quantity to the wishlist was made
					if( !empty($_REQUEST[ 'wl_quantity' ] ) ) {
						//The wp_quantity value is set, so we want to increment the quantity in the session now

// If there's already a value for quantity set in the session, append the new value - else replace it
						if( !empty($_SESSION[ 'wishlist' ][ 'product_quantity' ] ) ) :
							$_SESSION[ 'wishlist' ][ 'product_quantity' ] = $_SESSION[ 'wishlist' ][ 'product_quantity' ] + intval( $_REQUEST[ 'wl_quantity' ] );
						else : 
							$_SESSION[ 'wishlist' ][ 'product_quantity' ] = intval( $_REQUEST[ 'wl_quantity' ] );
endif;
					}
?>