Functions of the WordPress API to Avoid

The following functions can be rightly called "evil" as they can easily break other code in your site/app and/or can be broken by code changes made elsewhere in your site/app.

The Loop

Avoid The Loop and all functions related to The Loop.

Here is an example of The Loop code:

if ( have_posts() ):
    while ( have_posts() ):
    the_post(); ?>
    <h1><?php the_title(); ?></h1>
        <?php the_content(); 
    endwhile;
endif;

Use a List object rather than The Loop.

$articles = YourApp_Article::get_list();
if ( $articles->count() ):
    foreach( $articles as $article ): ?>
        <h1><?php article->the_title(); ?></h1>
        <?php article->the_content(); 
    endforeach;
endif;

Using List objects is more robust as they do not rely on global variables in the same manner as does The Loop.

wp_reset_postdata()

The wp_reset_postdata() function arbitrarily sets global variables and is typically used to restore an environment after a setup_postdata().

But wp_reset_postdata() does not actually restore what came before, it sets the environment to a default state instead. If there was a variable in global scope that conflicts, (such as an object stored in a variable named $page), calling wp_reset_postdata() breaks code elsewhere.

Here is an example of how wp_reset_postdata() might be used (provide a better example):

function get_content_html() {
    setup_postdata( $this->post() );
    $content = get_the_content();
    wp_reset_postdata();
    return $content;
}

Using WPLib we can instead do this:

function get_content_html() {
    $saved = $this->setup_postdata();
    $content = get_the_content();
    $this->restore_postdata( $saved );
    return $content;
}

And that is much less likely to break surrounding code.

Of course wp_reset_postdata() is a recommended WordPress API function but this is a perfect example of how WPLib can improve robustness of your WordPress applications.

Template Tags that Rely on Global Data.

Template Tags that are Purely Evil

Template Tags that are Evil If Unqualified

These template tags are okay to use if qualified with a $post or $post_id or other relevant parameter.

However, it is generally better to use WPLib's instance methods than these functions because the former are designed to be robust where some of the template tags have issues with accessing or updating global variables.

query_posts()