Custom Fields

function woo_add_custom_general_fields() {

	global $woocommerce, $post;
        echo '<div class="options_group">';
	
	// Text Field
	woocommerce_wp_text_input( 
		array( 
			'id'          => '_text_field', 
			'label'       => __( 'My Text Field', 'woocommerce' ), 
			'placeholder' => 'https://',
			'desc_tip'    => 'true',
			'description' => __( 'Enter the custom value here.', 'woocommerce' ) 
		)
	);
	
	// Number Field
	woocommerce_wp_text_input( 
		array( 
			'id'                => '_number_field', 
			'label'             => __( 'My Number Field', 'woocommerce' ), 
			'placeholder'       => '', 
			'description'       => __( 'Enter the custom value here.', 'woocommerce' ),
			'type'              => 'number', 
			'custom_attributes' => array(
					'step' 	=> 'any',
					'min'	=> '0'
			) 
		)
	);
	
	echo '</div>';
}

// Save Fields
add_action( 'woocommerce_process_product_meta', 'woo_add_custom_general_fields_save' );

function woo_add_custom_general_fields_save( $post_id ){
	
	// Text Field
	$woocommerce_text_field = isset($_POST['_text_field']) ? $_POST['_text_field'] : '';
	if( !empty( $woocommerce_text_field ) )
		update_post_meta( $post_id, '_text_field', esc_attr( $woocommerce_text_field ) );
		
	// Number Field
	$woocommerce_number_field = isset($_POST['_number_field']) ? $_POST['_number_field'] : '';
	if( !empty( $woocommerce_number_field ) )
		update_post_meta( $post_id, '_number_field', esc_attr( $woocommerce_number_field ) );
	
}