Add a "LIKE = typename" clause to CREATE TYPE for base types. This allows

the basic representational details (typlen, typalign, typbyval, typstorage)
to be copied from an existing type rather than listed explicitly in the
CREATE TYPE command.  The immediate reason for this is to provide a simple
solution for add-on modules that want to define types represented as int8,
float4, or float8: as of 8.4 the appropriate PASSEDBYVALUE setting is
platform-specific and so it's hard for a SQL script to know what to do.

This patch fixes the contrib/isn breakage reported by Rushabh Lathia.

contrib/isn/isn.sql.in

-/* $PostgreSQL: pgsql/contrib/isn/isn.sql.in,v 1.8 2007/11/13 04:24:28 momjian Exp $ */
+/* $PostgreSQL: pgsql/contrib/isn/isn.sql.in,v 1.9 2008/11/30 19:01:29 tgl Exp $ */
 
 -- Adjust this setting to control where the objects get created.
 SET search_path = public;
@@ -28,9 +28,7 @@ CREATE OR REPLACE FUNCTION ean13_out(ean13)
 CREATE TYPE ean13 (
 	INPUT = ean13_in,
 	OUTPUT = ean13_out,
-	INTERNALLENGTH = 8,
-	ALIGNMENT = double,
-	STORAGE = PLAIN
+	LIKE = pg_catalog.int8
 );
 COMMENT ON TYPE ean13
 	IS 'International European Article Number (EAN13)';
@@ -48,9 +46,7 @@ CREATE OR REPLACE FUNCTION ean13_out(isbn13)
 CREATE TYPE isbn13 (
 	INPUT = isbn13_in,
 	OUTPUT = ean13_out,
-	INTERNALLENGTH = 8,
-	ALIGNMENT = double,
-	STORAGE = PLAIN
+	LIKE = pg_catalog.int8
 );
 COMMENT ON TYPE isbn13
 	IS 'International Standard Book Number 13 (ISBN13)';
@@ -68,9 +64,7 @@ CREATE OR REPLACE FUNCTION ean13_out(ismn13)
 CREATE TYPE ismn13 (
 	INPUT = ismn13_in,
 	OUTPUT = ean13_out,
-	INTERNALLENGTH = 8,
-	ALIGNMENT = double,
-	STORAGE = PLAIN
+	LIKE = pg_catalog.int8
 );
 COMMENT ON TYPE ismn13
 	IS 'International Standard Music Number 13 (ISMN13)';
@@ -88,9 +82,7 @@ CREATE OR REPLACE FUNCTION ean13_out(issn13)
 CREATE TYPE issn13 (
 	INPUT = issn13_in,
 	OUTPUT = ean13_out,
-	INTERNALLENGTH = 8,
-	ALIGNMENT = double,
-	STORAGE = PLAIN
+	LIKE = pg_catalog.int8
 );
 COMMENT ON TYPE issn13
 	IS 'International Standard Serial Number 13 (ISSN13)';
@@ -110,9 +102,7 @@ CREATE OR REPLACE FUNCTION isn_out(isbn)
 CREATE TYPE isbn (
 	INPUT = isbn_in,
 	OUTPUT = isn_out,
-	INTERNALLENGTH = 8,
-	ALIGNMENT = double,
-	STORAGE = PLAIN
+	LIKE = pg_catalog.int8
 );
 COMMENT ON TYPE isbn
 	IS 'International Standard Book Number (ISBN)';
@@ -130,9 +120,7 @@ CREATE OR REPLACE FUNCTION isn_out(ismn)
 CREATE TYPE ismn (
 	INPUT = ismn_in,
 	OUTPUT = isn_out,
-	INTERNALLENGTH = 8,
-	ALIGNMENT = double,
-	STORAGE = PLAIN
+	LIKE = pg_catalog.int8
 );
 COMMENT ON TYPE ismn
 	IS 'International Standard Music Number (ISMN)';
@@ -150,9 +138,7 @@ CREATE OR REPLACE FUNCTION isn_out(issn)
 CREATE TYPE issn (
 	INPUT = issn_in,
 	OUTPUT = isn_out,
-	INTERNALLENGTH = 8,
-	ALIGNMENT = double,
-	STORAGE = PLAIN
+	LIKE = pg_catalog.int8
 );
 COMMENT ON TYPE issn
 	IS 'International Standard Serial Number (ISSN)';
@@ -170,9 +156,7 @@ CREATE OR REPLACE FUNCTION isn_out(upc)
 CREATE TYPE upc (
 	INPUT = upc_in,
 	OUTPUT = isn_out,
-	INTERNALLENGTH = 8,
-	ALIGNMENT = double,
-	STORAGE = PLAIN
+	LIKE = pg_catalog.int8
 );
 COMMENT ON TYPE upc
 	IS 'Universal Product Code (UPC)';

doc/src/sgml/ref/create_type.sgml

 <!--
-$PostgreSQL: pgsql/doc/src/sgml/ref/create_type.sgml,v 1.78 2008/11/14 10:22:46 petere Exp $
+$PostgreSQL: pgsql/doc/src/sgml/ref/create_type.sgml,v 1.79 2008/11/30 19:01:29 tgl Exp $
 PostgreSQL documentation
 -->
 
@@ -39,6 +39,7 @@ CREATE TYPE <replaceable class="parameter">name</replaceable> (
     [ , PASSEDBYVALUE ]
     [ , ALIGNMENT = <replaceable class="parameter">alignment</replaceable> ]
     [ , STORAGE = <replaceable class="parameter">storage</replaceable> ]
+    [ , LIKE = <replaceable class="parameter">like_type</replaceable> ]
     [ , CATEGORY = <replaceable class="parameter">category</replaceable> ]
     [ , PREFERRED = <replaceable class="parameter">preferred</replaceable> ]
     [ , DEFAULT = <replaceable class="parameter">default</replaceable> ]
@@ -290,6 +291,21 @@ CREATE TYPE <replaceable class="parameter">name</replaceable>
    <literal>external</literal> items.)
   </para>
 
+  <para>
+   The <replaceable class="parameter">like_type</replaceable> parameter
+   provides an alternative method for specifying the basic representation
+   properties of a data type: copy them from some existing type. The values of
+   <replaceable class="parameter">internallength</replaceable>,
+   <replaceable class="parameter">passedbyvalue</replaceable>,
+   <replaceable class="parameter">alignment</replaceable>, and
+   <replaceable class="parameter">storage</replaceable> are copied from the
+   named type.  (It is possible, though usually undesirable, to override
+   some of these values by specifying them along with the <literal>LIKE</>
+   clause.)  Specifying representation this way is especially useful when
+   the low-level implementation of the new type <quote>piggybacks</> on an
+   existing type in some fashion.
+  </para>
+
   <para>
    The <replaceable class="parameter">category</replaceable> and
    <replaceable class="parameter">preferred</replaceable> parameters can be
@@ -524,6 +540,22 @@ CREATE TYPE <replaceable class="parameter">name</replaceable>
     </listitem>
    </varlistentry>
 
+   <varlistentry>
+    <term><replaceable class="parameter">like_type</replaceable></term>
+    <listitem>
+     <para>
+      The name of an existing data type that the new type will have the
+      same representation as.  The values of
+      <replaceable class="parameter">internallength</replaceable>,
+      <replaceable class="parameter">passedbyvalue</replaceable>,
+      <replaceable class="parameter">alignment</replaceable>, and
+      <replaceable class="parameter">storage</replaceable>
+      are copied from that type, unless overridden by explicit
+      specification elsewhere in this <command>CREATE TYPE</> command.
+     </para>
+    </listitem>
+   </varlistentry>
+
    <varlistentry>
     <term><replaceable class="parameter">category</replaceable></term>
     <listitem>