Re: Do we want a hashset type?

similar to (int[] || int4) and (int4 || int[])
should we expect ('{1,2}'::int4hashset || 3) == (3 ||
'{1,2}'::int4hashset) == (select hashset_add('{1,2}'::int4hashset,3)); *?*

The following is the general idea on how to make it work by looking at
similar code....
CREATE OPERATOR || (
leftarg = int4hashset,
rightarg = int4,
function = int4hashset_add,
commutator = ||
);

CREATE OR REPLACE FUNCTION int4_add_int4hashset(int4, int4hashset)
RETURNS int4hashset
LANGUAGE sql
IMMUTABLE PARALLEL SAFE STRICT COST 1
RETURN $2 || $1;

CREATE OPERATOR || (
leftarg = int4,
rightarg = int4hashset,
function = int4_add_int4hashset,
commutator = ||
);
while creating an operator. I am not sure how to specify
NEGATOR,RESTRICT,JOIN clause.
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also. I think the following query should return one row only? but now it
doesn't.
select hashset_cmp('{1,2}','{2,1}')
union
select hashset_cmp('{1,2}','{1,2,1}')
union
select hashset_cmp('{1,2}','{1,2}');
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similar to elem_contained_by_range, range_contains_elem. we should already
consider the operator *<@* and @*>? *

CREATE OR REPLACE FUNCTION elem_contained_by_hashset(int4, int4hashset)
RETURNS bool
LANGUAGE sql
IMMUTABLE PARALLEL SAFE STRICT COST 1
RETURN hashset_contains ($2,$1);

Is the integer contained in the int4hashset?
integer <@ int4hashset → boolean
1 <@ int4hashset'{1,7}' → t

CREATE OPERATOR <@ (
leftarg = integer,
rightarg = int4hashset,
function = elem_contained_by_hashset
);

int4hashset @> integer → boolean
Does the int4hashset contain the element?
int4hashset'{1,7}' @> 1 → t

CREATE OPERATOR @> (
leftarg = int4hashset,
rightarg = integer,
function = hashset_contains
);
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