[wp-trac] [WordPress Trac] #43941: Add default value to register meta

[WordPress Trac]

#43941: Add default value to register meta
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 Reporter:  spacedmonkey                |       Owner:  spacedmonkey
     Type:  enhancement                 |      Status:  assigned
 Priority:  normal                      |   Milestone:  5.0
Component:  Options, Meta APIs          |     Version:  4.6
 Severity:  normal                      |  Resolution:
 Keywords:  has-patch needs-unit-tests  |     Focuses:  rest-api
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Comment (by flixos90):

 Replying to [comment:6 spacedmonkey]:

 > I am not sure I like this idea. I personally hate conditional filters in
 core, it is means that developers have to route through code and fine out
 when filters are fired. This is confusing. Firing both filters here does
 the same thing functionally, not sure why we need to change it.

 We decided earlier for #38323 that only the subtype-specific filters
 should fire if used, with the other ones only executed as fallback. This
 is the case for both sanitize and auth filters, and it should be the same
 here.

 > So my original patch did this, but I couldn't get it working without
 with either,
 > - Using an an anonymous function, which are not supported in PHP 5.2
 > - Using `create_function`, which is not supported in later versions of
 PHP.
 > - Create two new functions, that are single use. This feels a little
 pointless and weird. Might just be me. Am I missing something here?

 I agree that this would be far easier if we had anonymous functions, but
 it's also okay to introduce a one-off function for that. Please check how
 this is handled for options (see `filter_default_option()`).

 > > get_metadata_default() as well as the two filters need to be aware of
 the value of $single, in order to allow developers full flexibility in
 handling this. The default value may need to be different, depending on
 how a meta value is requested.
 >
 > How do you intend this works? So in register_meta, should it have
 `default_single` and `default_multi`. If so, if `default_multi` isn't set,
 does it fallback to `default_single`.This doesn't feel right. I personally
 think of defaults as defaulting a single value. If anything, I wouldn't
 support defaulting the multiple values.

 I absolutely agree we should not have two default values. However I think
 we need to think of the filters and the registered default value a bit
 more separately. The filters themselves need to be aware of how the meta
 value is requested. However, when registering, there should only be a
 single `default` value. For example, if a meta key is registered with
 `single => false` and `default => array( 'my_value, 'my_value_2' )` and
 someone calls `get_metadata()` with `$single` set to true, the default
 filter callback would need to handle this, and only return the first value
 from the array (which here would be `my_value`). It is unfortunate that we
 still have this `$single` parameter although it could now automatically be
 handled. But since it is there, we definitely need to ensure the returned
 default value takes this into account.

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Ticket URL: <https://core.trac.wordpress.org/ticket/43941#comment:7>
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