diff options
| -rw-r--r-- | doc/src/sgml/extend.sgml | 21 |
1 files changed, 17 insertions, 4 deletions
diff --git a/doc/src/sgml/extend.sgml b/doc/src/sgml/extend.sgml index 74130dc51d1..afd2b8f9fcc 100644 --- a/doc/src/sgml/extend.sgml +++ b/doc/src/sgml/extend.sgml @@ -225,10 +225,12 @@ <type>anyarray</type> positions must be an array whose elements are the same type appearing in the <type>anyelement</type> positions. Similarly, if there are positions declared <type>anyrange</type> - and others declared <type>anyelement</type>, the actual range type in - the <type>anyrange</type> positions must be a range whose subtype is - the same type appearing in the <type>anyelement</type> positions. - <type>anynonarray</> is treated exactly the same as <type>anyelement</>, + and others declared <type>anyelement</type> or <type>anyarray</type>, + the actual range type in the <type>anyrange</type> positions must be a + range whose subtype is the same type appearing in + the <type>anyelement</type> positions and the same as the element type + of the <type>anyarray</type> positions. + <type>anynonarray</type> is treated exactly the same as <type>anyelement</type>, but adds the additional constraint that the actual type must not be an array type. <type>anyenum</> is treated exactly the same as <type>anyelement</>, @@ -259,6 +261,17 @@ </para> <para> + In most cases, the parser can infer the actual data type for a + polymorphic result type from arguments that are of a different + polymorphic type; for example <type>anyarray</type> can be deduced + from <type>anyelement</type> or vice versa. The exception is that a + polymorphic result of type <type>anyrange</type> requires an argument + of type <type>anyrange</type>; it cannot be deduced + from <type>anyarray</type> or <type>anyelement</type> arguments. This + is because there could be multiple range types with the same subtype. + </para> + + <para> Note that <type>anynonarray</> and <type>anyenum</> do not represent separate type variables; they are the same type as <type>anyelement</type>, just with an additional constraint. For |