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Re: [Patch] Make svn_tristate_t compatible with svn_boolean_t

From: Julian Foad <julian.foad_at_wandisco.com>
Date: Thu, 04 Nov 2010 11:51:36 +0000

On Thu, 2010-11-04, Stefan Fuhrmann wrote:
> Hi there,
>
> after stumbling twice over this issue, I ran grep
> and found that the current usage of svn_tristate_t
> does not depend on the actual numerical values
> used for its states.
>
> Therefore, I propose to define svn_tristate_false
> equal to FALSE and svn_tristate_true equal to
> TRUE. That way, we can compare booleans with
> tristates and assign booleans to tristates. Without
> that, we need to write code like
>
> if ((get_some_bool() ? svn_tristate_true : svn_tristate_false) ==
> get_a_tristate())
> ...
>
> Also, the following will compile without warning but
> requires the patch to do what was intended:
>
> // FALSE becomes "unknown", TRUE becomes "false"
> svn_tristate_t my_tristate = get_some_bool();
>
> -- Stefan^2.
>
> [[[
> Make svn_tristate_t mainly compatible to svn_boolean_t
> by making its numerical values match the ones used for
> svn_boolean_t.
>
> * subversion/include/svn_types.h
> (svn_tristate_t): define *_true and *_false in terms of
> the svn_boolean_t values TRUE and FALSE, respectively.
> ]]]

It seems sensible to have the set of values either match where they
overlap (like you're suggesting), or be totally incompatible (e.g. the
set of tristate values being 2/3/4, or the tristate data type being
incompatible with "int").

If the values match, then there is no need for the enumerators
"svn_tristate_false" and "svn_tristate_true", since "FALSE" and "TRUE"
can be used instead. If the idea is that these values are compatible,
then we *should* delete the "svn_tristate_true/false" names and use the
existing names for them, and not have the ambiguity of which name to
use.

As Bert said, it's not always safe to assign or compare what we call a
"Boolean" value directly with an svn_tristate_t value, because we can't
always guarantee that "true" is represented by "1". But often it would
be safe. :-/

- Julian
Received on 2010-11-04 12:52:21 CET

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