WordPress plugin example code to correctly set a custom number of posts to display per page, for specific types of views

cws-posts-per-page.php

<?php
/*
Plugin Name: CWS Posts Per Page
Version: 0.1
Description: Sets a custom number of posts to display per page, for specific types of views
Author: Mark Jaquith
Author URI: http://coveredwebservices.com/
*/

class CWS_Posts_Per_Page_Plugin {
	public static $instance;
	public $posts_per_page = array(
		'day' => 9999,
		'month' => 30,
		'search' => 30,
		'year' => 30,
		'author' => 30,
		'category' => 30,
	);
	public $ran = false;

	public function __construct() {
		self::$instance = $this;
		// We use parse_request, because that only runs on primary WP queries. We use that to add the parse_query filter
		add_action( 'parse_request', array( $this, 'parse_request' ) );
	}

	public function parse_request() {
		add_action( 'parse_query', array( $this, 'parse_query' ) );
	}

	public function parse_query( $q ) {
		if ( $this->ran )
				return $q;
		foreach ( $this->posts_per_page as $flag => $ppp ) {
			$flag = 'is_' . $flag;
			if ( $q->$flag ) {
				$q->set( 'posts_per_page', $ppp );
				break;
			}
		}

		// If you want to add more logic, do it here

		// Mark this code as having run, so it doesn't run more than once
		$this->ran = true;
		return $q;
	}

}

new CWS_Posts_Per_Page_Plugin;

Yeah, so you could replace $this with self or __CLASS__ and make all the properties and methods static.

Ah. Just a syntactic preference. self::$foo looks uglier and less familiar than $this->foo to me.

Can't argue with that. :)