From b2ffdfcc33ae6d002395e7c234c2aa3249149015 Mon Sep 17 00:00:00 2001
From: Florents Tselai <florents.tselai@gmail.com>
Date: Wed, 9 Oct 2024 21:46:37 +0300
Subject: [PATCH v2 2/2] Add note on NULL. Update example to use text*

---
 doc/src/sgml/xfunc.sgml | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/doc/src/sgml/xfunc.sgml b/doc/src/sgml/xfunc.sgml
index eb26120def..ee4330a9cc 100644
--- a/doc/src/sgml/xfunc.sgml
+++ b/doc/src/sgml/xfunc.sgml
@@ -2397,6 +2397,7 @@ PG_FUNCTION_INFO_V1(funcname);
     (or its <literal>Oid</literal> in some cases),
     and actual arguments should be supplied as <literal>Datum</literal>s.
     They always return <literal>Datum</literal>.
+    Note that neither arguments nor result are allowed to be NULL.
     </para>
 
     <para>
@@ -2412,6 +2413,7 @@ PG_FUNCTION_INFO_V1(funcname);
     you can use <function>DatumGetTextPP(X)</function>.
     If your extension defines additional types,
     it is usually convenient to define similar macros for these types too.
+    You can use <function>PointerGetDatum(x)</function> to turn pointers of standard types into <literal>Datum</literal>
     </para>
 
     <para>
@@ -2520,14 +2522,16 @@ PG_FUNCTION_INFO_V1(t_starts_with);
 Datum
 t_starts_with(PG_FUNCTION_ARGS)
 {
-    Datum t1 = PG_GETARG_DATUM(0);
-    Datum t2 = PG_GETARG_DATUM(1);
-    bool  bool_res;
+    text *t1 = PG_GETARG_TEXT_PP(0);
+    text *t2 = PG_GETARG_TEXT_PP(1);
+    bool  result;
 
-    Datum datum_res = DirectFunctionCall2(text_starts_with, t1, t2);
-    bool_res = DatumGetBool(datum_res);
+    result = DatumGetBool(
+                  DirectFunctionCall2(text_starts_with,
+                                      PointerGetDatum(t1),
+                                      PointerGetDatum(t2));
 
-    PG_RETURN_BOOL(bool_res);
+    PG_RETURN_BOOL(result);
 }
 ]]>
 </programlisting>
-- 
2.39.5 (Apple Git-154)