Colon operator in PHP

问题

This is part of the wordpress code and I don't understand it:

if     ( is_404()            && $template = get_404_template()            ) :
elseif ( is_search()         && $template = get_search_template()         ) :
elseif ( is_tax()            && $template = get_taxonomy_template()       ) :
elseif ( is_front_page()     && $template = get_front_page_template()     ) :
elseif ( is_home()           && $template = get_home_template()           ) :
elseif ( is_attachment()     && $template = get_attachment_template()     ) :
    remove_filter('the_content', 'prepend_attachment');
elseif ( is_single()         && $template = get_single_template()         ) :
elseif ( is_page()           && $template = get_page_template()           ) :
elseif ( is_category()       && $template = get_category_template()       ) :
elseif ( is_tag()            && $template = get_tag_template()            ) :
elseif ( is_author()         && $template = get_author_template()         ) :
elseif ( is_date()           && $template = get_date_template()           ) :
elseif ( is_archive()        && $template = get_archive_template()        ) :
elseif ( is_comments_popup() && $template = get_comments_popup_template() ) :
elseif ( is_paged()          && $template = get_paged_template()          ) :
else :
    $template = get_index_template();
endif;

A colon can replace a curly bracket in PHP. So if I substitute the colons, I get this:

if     ( is_404()            && $template = get_404_template()            ) {
   elseif ( is_search()         && $template = get_search_template()         ) {
      elseif ( is_tax()            && $template = get_taxonomy_template()       ) {
      ...
      }
   }
}
else

Makes no sense to me, because each elseif is missing its opening if.

回答1:

Reggie,

colons in if/else statements in PHP : it's NOT about replacing braces but a PAIR of braces.

Example :

if ($a) : doThis();
elseif ($b) : doThat();
else : doTheOther();
endif;

would become

if ($a) { doThis(); }
elseif ($b) { doThat(); }
else { doTheOther(); }

OR (since it's just one statement and not a block of statements)

if ($a) doThis();
elseif($b) doThat();
else doTheOther();

---

Reference : Alternative Syntax for Control Structures

---

As for this specific piece of code :

if     ( is_404()            && $template = get_404_template()            ) :
elseif ( is_search()         && $template = get_search_template()         ) :
elseif ( is_tax()            && $template = get_taxonomy_template()       ) :

it translates to

if     ( is_404()            && $template = get_404_template()            )  
    { /* DO NOTHING */ }
elseif ( is_search()         && $template = get_search_template()         )  
    { /* DO NOTHING */ }

Hint : The elseif statement does NOT include the other elseif statements. (like elseif ($a) { elseif($b) {} })

来源：https://stackoverflow.com/questions/10054345/colon-operator-in-php