Exclusion constraints on overlapping text arrays?

Hi. Using 9.6.14, I was setting up a table with this:

EXCLUDE using gist (EXCLUDE using gist (grant_number_codes with &&)

Where grant_numbers is a varchar[]. I get this error:

ERROR: data type character varying[] has no default operator class for
access method "gist"
HINT: You must specify an operator class for the index or define a default
operator class for the data type.

I did some Googling, and it looks like you could do this for integer arrays
with the intarray extension. I didn't see anything I'd recognize as an
equivalent for varchar (or text) arrays. Is there any way to do this now?
And if not, is there much prospect of this being implemented at some point?

I found a couple of old threads about this. Not sure if they are still
relevant, but listed below.

Also, on a side note, I tried using grant_number_codes::text[] with &&, but
that got a syntax error. Does that mean casting isn't allowed at all in
these constraints?

Thanks in advance,
Ken

1) This 2014 thread asked about this:

*array exclusion constraints*
https://www.postgresql.org/message-id/flat/20141113183843.E8AC620362%40smtp.hushmail.com

and pointed toward this 2013 discussion:

*Todo item: Support amgettuple() in GIN*
https://www.postgresql.org/message-id/flat/5297DC17.7000608%40proxel.se

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