Solution to Code Challenge 1 from "Refactoring Tweaks Workbook"

code-challenge-1.php

// # Code Challenge 1, from “Refactoring Tweaks Workbook” by Tonya Mork ( 2016, LeanPub (https://leanpub.com/littlegreenbookofrefactoringtweaks-workbook) ).  

// ## Original code to be refactored

/**
 * Check if custom post type exists, to provide data
 */
function prefix_is_post_type( string $type, int $post_id ) {
    global $wp_query;
    if($type == get_post_type($wp_query->post->ID)) return true;
    return false;
}

// ### Discussion

/** 
 *  The function above calls the global variable `$wp_query`. Global variables are both readable and writable. 
 *  If any values within the global variable are rewritten, this could affect the behavior of the `$wp_query` object through 
 *  the rest of the application, and require time and effort to debug.
 *
 *  The way to avoid interacting with the global variable is to build an API that abstracts away access to the global object.
 */


// ## Refactored code

/**
 * Evaluate post_type for a given post_id. ( Refactored original function. )
 *
 * @since 1.0.0
 *
 * @param string $type      The post_type to be evaluated.
 * @param int    $post_id   The post_id 
 *
 * @return bool  Evaluation of post_type comparison.  
 */
function prefix_is_post_type( string $type, int $post_id ) {
	$post_type = get_the_post_type( $post_id );
	if ( $type == $post_type ) return true;

	return false;
}

/**
 * Get post_type from the post object.
 *
 * @since 1.0.0
 *
 * @param  int $post_id The post id.
 * @return string|null  The post_type attribute.
 */
function get_the_post_type( int $post_id = 0 ) {
	if ( ! post_id ) {
		return;
	}
	return get_post_attribute( 'post_type', $post_id );
}

/**
 * Get post attribute.
 *
 * @since 1.0.0
 *
 * @param string $attribute Name of the post attribute.
 * @param int    $post_id   The post ID.
 *
 * @return string|null Attribute name.
 */
function get_post_attribute( string $attribute, int $post_id = 0 ) {
	if ( ! post_id ) {
		return;
	}
	$post = get_post( $post_id );
	return $post->$attribute;
}

// ### Discussion

/**
 *  The refactoring solution above creates an API to interact with the `$post` object ( an instance of the WP_Post class ),
 *  and retrieve attributes ( properties ). The function `get_post_attribute()` interacts directly with the `$post` object 
 *  to retrieve a specific attribute. The function `get_the_post_type()` is a wrapper for `get_post_attribute()`, and returns 
 *  the attribute passed as an argument. 
 * 
 *  The refactored function `prefix_is_post_type()` then performs its single responsiblity; to evaluate whether the actual 
 *  post_type ( argument `$type` ) is equal to the expected post_type. 
 */