String concatenation operator which keeps trailing spaces in CHAR(n) columns

How to create string concatenation operator which preserves trailing spaces
on CHAR(n) type columns ?

I tried code below, but it returns AB (without spaces).
How to force it to return A B (keep space after A) ?

Andrus.

CREATE OR REPLACE FUNCTION public.stringconcat(left text, right text)
RETURNS text
LANGUAGE sql IMMUTABLE
AS $BODY$
SELECT concat($1, $2) ;
$BODY$;

CREATE OPERATOR public.+ (
leftarg = text,
rightarg = text,
procedure = public.stringconcat
);

create temp table test (col1 char(2)) on commit drop;
insert into test values ('A');
select col1 + 'B'
from test;

I posted similar question also in

http://stackoverflow.com/questions/24975118/how-to-create-string-concatenation-operator-which-preserves-trailing-spaces-in-c