Sorry for being late to the party
I started looking at the thread about "Generic type subscripting" and am wondering,
why does it take the approach of modifying pg_type and modifying lots of internal
functions, when instead it could be defined in a much lighter and less intrusive way
as an operator, probably by reserving a dedicated operator name
CREATE OPERATOR [...] (PROCEDURE = json_object_field, LEFTARG=jsonb, RIGHTARG=text);
CREATE OPERATOR [...] (PROCEDURE = jsonb_array_element, LEFTARG=jsonb, RIGHTARG=int);
This might put more work on the writers of actual subscription operators, but if we are looking at diverse new types, it may also be, that writing operator functions is even easier than learning a full new skillset for writing "subscripting functions"
Defining "subscripting" as an operator does still require changes to how current subscripting operations are parsed, but even there I am not sure it would be more complex, as all the parser has to do is to determine that it is a subscripting operation and then delegate to the corresponding operator.
Also, there is a problem of what to do with element (or or even slice) assignements, as there require three arguments.
I see two possibilities
1) add a third "ARG" to the CREATE OPERATOR syntax, maybe VALUEARG
2) use composite types - so for
jsonb1[int1] = jsonb2
the operator would be defined by first defining a
CREATE TYPE intkey_and_jsonvalue as (key int, value jsonb)
and then using this in
CREATE OPERATOR [...] (PROCEDURE = jsonb_set_key, LEFTARG=jsonb, RIGHTARG=intkey_and_jsonvalue)
Cheers
Hannu