Downgrade implicit casts to text to be assignment-only, except for the ones

from the other string-category types; this eliminates a lot of surprising
interpretations that the parser could formerly make when there was no directly
applicable operator.

Create a general mechanism that supports casts to and from the standard string
types (text,varchar,bpchar) for *every* datatype, by invoking the datatype's
I/O functions.  These new casts are assignment-only in the to-string direction,
explicit-only in the other, and therefore should create no surprising behavior.
Remove a bunch of thereby-obsoleted datatype-specific casting functions.

The "general mechanism" is a new expression node type CoerceViaIO that can
actually convert between *any* two datatypes if their external text
representations are compatible.  This is more general than needed for the
immediate feature, but might be useful in plpgsql or other places in future.

This commit does nothing about the issue that applying the concatenation
operator || to non-text types will now fail, often with strange error messages
due to misinterpreting the operator as array concatenation.  Since it often
(not always) worked before, we should either make it succeed or at least give
a more user-friendly error; but details are still under debate.

Peter Eisentraut and Tom Lane

contrib/cube/README.cube

@@ -236,10 +236,6 @@ cube_distance(cube, cube) returns double
   cube_distance returns the distance between two cubes. If both cubes are
   points, this is the normal distance function.
 
-cube(text) returns cube
-  cube takes text input and returns a cube. This is useful for making cubes
-  from computed strings.
-
 cube(float8) returns cube
   This makes a one dimensional cube with both coordinates the same.
   If the type of the argument is a numeric type other than float8 an

contrib/cube/cube.c

@@ -1,5 +1,5 @@
 /******************************************************************************
-  $PostgreSQL: pgsql/contrib/cube/cube.c,v 1.32 2007/03/07 21:21:11 teodor Exp $
+  $PostgreSQL: pgsql/contrib/cube/cube.c,v 1.33 2007/06/05 21:31:03 tgl Exp $
 
   This file contains routines that can be bound to a Postgres backend and
   called by the backend in the process of processing queries.  The calling
@@ -173,18 +173,6 @@ cube_in(PG_FUNCTION_ARGS)
 	PG_RETURN_NDBOX(result);
 }
 
-/* Allow conversion from text to cube to allow input of computed strings */
-/* There may be issues with toasted data here. I don't know enough to be sure.*/
-Datum
-cube(PG_FUNCTION_ARGS)
-{
-	char	   *cstring;
-
-	cstring = DatumGetCString(DirectFunctionCall1(textout, PointerGetDatum(PG_GETARG_TEXT_P(0))));
-
-	PG_RETURN_DATUM(DirectFunctionCall1(cube_in, PointerGetDatum(cstring)));
-}
-
 
 /*
 ** Allows the construction of a cube from 2 float[]'s

contrib/cube/cube.sql.in

@@ -31,16 +31,6 @@ CREATE TYPE cube (
 
 COMMENT ON TYPE cube IS 'multi-dimensional cube ''(FLOAT-1, FLOAT-2, ..., FLOAT-N), (FLOAT-1, FLOAT-2, ..., FLOAT-N)''';
 
--- Convert from text to cube
-
-CREATE OR REPLACE FUNCTION cube(text) RETURNS cube
-AS 'MODULE_PATHNAME'
-LANGUAGE C IMMUTABLE STRICT;
-
-COMMENT ON FUNCTION cube(text) IS 'convert text to cube';
-
-CREATE CAST (text AS cube) WITH FUNCTION cube(text) AS ASSIGNMENT;
-
 --
 -- External C-functions for R-tree methods
 --

contrib/cube/expected/cube.out

@@ -826,7 +826,7 @@ SELECT cube_distance('(0)'::cube,'(.3,.4)'::cube);
 
 -- Test of cube function (text to cube)
 --
-SELECT cube('('||1||','||1.2||')');
+SELECT cube('(1,1.2)'::text);
    cube   
 ----------
  (1, 1.2)

contrib/cube/expected/cube_1.out

@@ -826,7 +826,7 @@ SELECT cube_distance('(0)'::cube,'(.3,.4)'::cube);
 
 -- Test of cube function (text to cube)
 --
-SELECT cube('('||1||','||1.2||')');
+SELECT cube('(1,1.2)'::text);
    cube   
 ----------
  (1, 1.2)

contrib/cube/expected/cube_2.out

@@ -826,7 +826,7 @@ SELECT cube_distance('(0)'::cube,'(.3,.4)'::cube);
 
 -- Test of cube function (text to cube)
 --
-SELECT cube('('||1||','||1.2||')');
+SELECT cube('(1,1.2)'::text);
    cube   
 ----------
  (1, 1.2)

contrib/cube/sql/cube.sql

@@ -223,7 +223,7 @@ SELECT cube_distance('(0)'::cube,'(.3,.4)'::cube);
 
 -- Test of cube function (text to cube)
 --
-SELECT cube('('||1||','||1.2||')');
+SELECT cube('(1,1.2)'::text);
 SELECT cube(NULL);
 
 -- Test of cube_dim function (dimensions stored in cube)

contrib/cube/uninstall_cube.sql

@@ -92,8 +92,4 @@ DROP FUNCTION cube_ne(cube, cube);
 
 DROP FUNCTION cube_eq(cube, cube);
 
-DROP CAST (text AS cube);
-
-DROP FUNCTION cube(text);
-
 DROP TYPE cube CASCADE;