[theme-reviewers] wrapping functions with if( ! function_exists() ) {…}

Ulrich Pogson grapplerulrich at gmail.com
Sat Oct 11 19:36:51 UTC 2014

Thanks Otto!

"The two version guideline was made back when versions were a bit more
spread out. Two versions now is like 6 months. I think being a bit lenient
on this one makes sense."
@tammie - Can we discuss this at the next Team Meeting?

On 11 October 2014 18:33, Otto <otto at ottodestruct.com> wrote:

> On Sat, Oct 11, 2014 at 10:48 AM, Ulrich Pogson <grapplerulrich at gmail.com>
> wrote:
>> The guidelines states: "Themes must not provide backward compatibility
>> for out-of-date WordPress versions (more than two prior major WordPress
>> versions – currently, that means versions prior to WordPress 3.8),
>> including using function_exists() conditional wrappers for current *WordPress
>> functions*." https://make.wordpress.org/themes/handbook/guidelines/
>> This is one thing we require but I could not find in the guidelines.
>> "Function calls must be placed inside callbacks and hooked into
>> appropriate actions or filters (such as after_setup_theme for Theme setup
>> functions, or widgets_init for Widgets/dynamic sidebar functions)"
>> The *theme functions* can be wrapped in a if( !function_exists()) {…}.
>> At the moment this is not required nor recommended.
>> Actually Chris wrote a good answer below Ottos:
>> http://wordpress.stackexchange.com/a/111318/17937
>> P.S I personally don't think every every theme function needs to be
>> wrapped in if( !function_exists()) {…} because depending on the function
>> you can just as well overwrite it with another function hooking into the
>> same hook. If the function was a bit more complex then it would be better
>> to make the function extendable with hooks and filters. So that child theme
>> could change single values instead of having to copy the whole function.
> The two version guideline was made back when versions were a bit more
> spread out. Two versions now is like 6 months. I think being a bit lenient
> on this one makes sense.
> As for the if(exists) check, I would recommend against it except when it's
> really necessary.
> Let's say a theme (parent) defines its functions like this:
> function whatever() {
> }
> add_action('init','whatever');
> Now, a child theme can override any function that is hooked into any hook
> like that by simply unhooking it in after_setup_theme and replacing it:
> function child_override() {
>    remove_action('init','whatever');
>    add_action('init','child_whatever');
> }
> add_action('after_setup_theme','child_override');
> The exception to this is parent functions that are themselves hooked
> into after_setup_theme. A child can't easily override these, because it has
> no hooks that fire earlier for it to unhook. And once the action is
> running, unhooking from inside it does nothing. So those particular
> functions, if any, should be pluggable using an if(exists) check.
> You can see this specific case with the twentyfourteen_setup function.
> It's not possible for a child theme to unhook that function, only to
> replace it by redefining it.
> Now, twentyfourteen actually makes a lot of its functions pluggable. The
> ones that it makes pluggable are one of the following:
> a) Hooked to after_setup_theme
> b) Called directly by something else in the theme
> (twentyfourteen_the_attached_image), so replacing them in a child is easier
> than having to replace their calling files too (image.php in that case).
> c) Used as a callback for something else (twentyfourteen_header_style), so
> replacing them is simpler than having to adjust the specific callback
> location in which they are added
> These are all good reasons for pluggable functions. The downside of
> pluggables is that they can only be replaced one time. A theme and a plugin
> cannot both override a pluggable. So, pluggables should really only be used
> when there's little other good avenues. Most of the time, if you're hooking
> a function to an action or filter, then it is possible for some other bit
> of code to unhook and replace it without a whole lot of difficulty, so
> making it pluggable is unnecessary.
> -Otto
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