Put a constraint on defcustom with variable type

Question

I have a defcustom with :type variable, and I would like to constrain the variable name to comply to a pattern.

How would I do that?

for instance let say I want the custom to only accept a variable name starting with some prefix.

Drew · Accepted Answer · 2017-09-21 14:02:27Z

4

Don't use type variable. Use type restricted-sexp.

The predicate checks for a symbolp that is boundp (i.e., a variable) and whose symbol-name is matched by your chosen prefix.

See the Elisp manual, node Composite Types.

answered Sep 21 '17 at 14:02

Drew

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Thanks Drew. I tried your solution, but for a strange reason the validating function is being called with nil except for the initial value. Besides the set handler is also called! Any idea why? – AdrieanKhisbe Sep 21 '17 at 21:11
Here is the code in question: gist.github.com/AdrieanKhisbe/81dbd538b6b8cca0b2dadd33ac24a6ed – AdrieanKhisbe Sep 21 '17 at 21:12
Looks like you accidentally used fboundp' in one place, instead of boundp'. – Drew Sep 21 '17 at 23:11
And you spot it right! Thanks a lot @Drew! :) – AdrieanKhisbe Sep 22 '17 at 11:44

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