Does it make sense to assign functions like is_paged() to a variable rather than using it multiple times?

2 comments

1. So, all query conditionals (is_paged, is_singular, etc) look something like this:

   function is_paged() {
       global $wp_query;
   
       if ( ! isset( $wp_query ) ) {
           _doing_it_wrong( __FUNCTION__, __( 'Conditional query tags do not work before the query is run. Before then, they always return false.' ), '3.1' );
           return false;
       }
   
       return $wp_query->is_paged();
   }
   

   Globalize $wp_query and call the corresponding method of the WP_Query object. In this case:

   <?php
   function is_paged() {
       return (bool) $this->is_paged;
   }
   

   The only database hit you incur is from when the WP_Query object is created, which happens anyway.

   Calling a function incurs a cost, so does using an if statement. Those costs on today’s hardware are nothing to really worry about.

   That said, if you find yourself doing a lot of conditional checking using the same function, you’re probably better off to evaluate the control flow of your program.

   Something like this:

   <?php
   if(is_paged() && 1 == get_query_var('some_query_var'))
   {
      // do stuff
   }
   else if(is_paged() && 2 == get_query_var('some_query_var'))
   {
      // do other stuff
   }
   

   Could become:

   <?php
   if(is_paged())
   {
      switch(get_query_var('some_query_var'))
      {
         case 1:
             // do stuff
             break;
         case 2:
             // do stuff
             break;
         default:
             // do stuff
             break;
       }
   }
   

   As a final word of advice, I would “cache” results of conditionals (or any other function call, within reason) within the same function if you need them more than once, but I wouldn’t cache something like a object property unless you really need that persist from method to method.

   Here’s a terrible example that (probably) doesn’t follow my advice above.

   <?php
   function wpse65916_stuff()
   {
       $paged = is_paged();
   
       if($paged)
       {
           // do stuff because paged
       }
   
       if($paged && /* some other condition */)
       {
           // do stuff
       }
   }
   

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2. No.

   Query conditionals are part of WordPress’ object cache, and incur no additional resources when called.

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