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Doc: fix mistaken reference to "PG_ARGNULL_xxx()" macro. 

This should of course be just "PG_ARGISNULL()".

Also reorder a couple of paras to make the discussion of PG_ARGISNULL
less disjointed.

Back-patch to v10 where the error was introduced.

Laurenz Albe and Tom Lane, per an anonymous docs comment

Discussion: https://postgr.es/m/158399487096.5708.10696365251766477013@wrigleys.postgresql.org
This commit is contained in:
Tom Lane 2020-03-13 12:49:10 -04:00
parent 340de72780
commit dbf95c843a
1 changed files with 10 additions and 10 deletions
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20
doc/src/sgml/xfunc.sgml
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@ -2237,9 +2237,9 @@ PG_FUNCTION_INFO_V1(funcname);
<para>
In a version-1 function, each actual argument is fetched using a
<function>PG_GETARG_<replaceable>xxx</replaceable>()</function>
macro that corresponds to the argument's data type. In non-strict
macro that corresponds to the argument's data type. (In non-strict
functions there needs to be a previous check about argument null-ness
using <function>PG_ARGNULL_<replaceable>xxx</replaceable>()</function>.
using <function>PG_ARGISNULL()</function>; see below.)
The result is returned using a
<function>PG_RETURN_<replaceable>xxx</replaceable>()</function>
macro for the return type.
@ -2401,14 +2401,6 @@ CREATE FUNCTION concat_text(text, text) RETURNS text
explicitly, using <function>PG_ARGISNULL()</function>.
</para>
<para>
At first glance, the version-1 coding conventions might appear to be just
pointless obscurantism, over using plain <literal>C</literal> calling
conventions. They do however allow to deal with <literal>NULL</literal>able
arguments/return values, and <quote>toasted</quote> (compressed or
out-of-line) values.
</para>
<para>
The macro <function>PG_ARGISNULL(<replaceable>n</replaceable>)</function>
allows a function to test whether each input is null. (Of course, doing
@ -2423,6 +2415,14 @@ CREATE FUNCTION concat_text(text, text) RETURNS text
this works in both strict and nonstrict functions.
</para>
<para>
At first glance, the version-1 coding conventions might appear
to be just pointless obscurantism, compared to using
plain <literal>C</literal> calling conventions. They do however allow
us to deal with <literal>NULL</literal>able arguments/return values,
and <quote>toasted</quote> (compressed or out-of-line) values.
</para>
<para>
Other options provided by the version-1 interface are two
variants of the