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Re: Difficulties with `purecopy' discarding text properties from strings

From: Stefan Monnier
Subject: Re: Difficulties with `purecopy' discarding text properties from strings
Date: Fri, 19 May 2017 15:22:50 -0400
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.0.50 (gnu/linux)

> Presumably there are good reasons for discarding text properties when
> purecopying strings.

I don't think so.

> Or, maybe, there was just no particular reason to amend the workings
> of `purecopy' when text properties came into existence.

I think that's what happens.

But wait a minute:
> I naively constructed such a defcustom, with text properties on the
> value option strings.

How exactly did you do that?  Using #("..." ...)
or using (propertize "..." ...)?

> After some debugging, I discover that defcustom strips those text
> properties off the strings.  It does this by using `purecopy' on these
> strings (in the function `custom-declare-variable').

But AFAICT custom-declare-variable only applies purecopy to its
`default` argument which is supposed to be an expression (which
evaluates to the intended value) rather than a value.  So if you use the
(propertize "..." ...)  form, the properties should not be stripped.

Or am I missing something?


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