Re: custom type tests

["Lennart Borgman (gmail)" <lennart.borgman@gmail.com>]

Lennart Borgman (gmail) wrote:
> Drew Adams wrote:
>> Does anyone know of code that deals with custom types in such a way 
>> that you
>> could test whether the type of a user option is compatible with a given
>> type?
>>
>> For instance, if a variable `foo' is of type `regexp' and `bar' is of 
>> type
>> `color', I would want a test for compatibility with type `string' to 
>> return
>> non-nil for each, since a regexp and a color are strings.
>>
>> As another example, if `foo' is of type `string', I would want a test for
>> compatibility with type (choice (const nil) string) to return non-nil, 
>> since
>> a string is in the union of all strings and {nil}.
>>
>> Any existing code that deals with subtypes this way? Any code that deals
>> with custom type tests, other than just `custom-variable-type' and 
>> (get __
>> 'custom-type)?
>>
>> I'm looking for code that would allow flexible type tests - subtyping, if
>> possible (see above), but also not differentiating between types such as
>> (choice (const :tag "toto" nil) string) and (choice (const nil) 
>> string) or
>> between (choice (choice (const nil) string) and (choice string (const 
>> nil)).
>>
>> Any pointers to pertinent code or doc are appreciated. Think of it 
>> this way:
>> Given a custom type, how can I find all user options that have that 
>> type (or
>> a compatible type, such as a subtype)?
> 
> 
> I do not know exactly, but the :match property of a widget has the 
> function you need. Look in cus-edit.el and wid-edit.el how this function 
> is built. It does not look very easy to find out however.


Thinking about it again, the code is in set-variable. Look for :match 
there.