doc: Suggest keeping record type descriptors private.

* doc/contributing.texi (Data Types and Pattern Matching): Add paragraph
about keeping RTDs private.

Suggested-by: Maxim Cournoyer <maxim.cournoyer@gmail.com>
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Ludovic Courtès 2023-10-05 16:15:24 +02:00
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@ -1308,6 +1308,17 @@ Guile Reference Manual}); pattern matching for records is better done
using @code{match-record} from @code{(guix records)}, which, unlike
@code{match}, verifies field names at macro-expansion time.
When defining a new record type, keep the @dfn{record type descriptor}
(RTD) private (@pxref{Records,,, guile, GNU Guile Reference Manual}, for
more on records and RTDs). As an example, the @code{(guix packages)}
module defines @code{<package>} as the RTD for package records but it
does not export it; instead, it exports a type predicate, a constructor,
and field accessors. Exporting RTDs would make it harder to change the
application binary interface (because code in other modules might be
matching fields by position) and would make it trivial for users to
forge records of that type, bypassing any checks we may have in the
official constructor (such as ``field sanitizers'').
@node Formatting Code
@subsection Formatting Code