Date: Thu, 14 Dec 2023 18:44:14 +0900 (JST)
Message-Id: <20231214.184414.2179134502876898942.kou@clear-code.com>
To: sawada.mshk@gmail.com
Cc: michael@paquier.xyz, zhjwpku@gmail.com, andrew@dunslane.net,
 nathandbossart@gmail.com, pgsql-hackers@postgresql.org
Subject: Re: Make COPY format extendable: Extract COPY TO format
 implementations
From: Sutou Kouhei <kou@clear-code.com>
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Hi,

In <CAD21AoCvjGserrtEU=UcA3Mfyfe6ftf9OXPHv9fiJ9DmXMJ2nQ@mail.gmail.com>
  "Re: Make COPY format extendable: Extract COPY TO format implementations" on Mon, 11 Dec 2023 10:57:15 +0900,
  Masahiko Sawada <sawada.mshk@gmail.com> wrote:

> IIUC we cannot create two same name functions with the same arguments
> but a different return value type in the first place. It seems to me
> to be an overkill to change such a design.

Oh, sorry. I didn't notice it.

> Another idea is to encapsulate copy_to/from_handler by a super class
> like copy_handler. The handler function is called with an argument,
> say copyto, and returns copy_handler encapsulating either
> copy_to/from_handler depending on the argument.

It's for using "${copy_format_name}" such as "json" and
"parquet" as a function name, right? If we use the
"${copy_format_name}" approach, we can't use function names
that are already used by tablesample method handler such as
"system" and "bernoulli" for COPY FORMAT name. Because both
of tablesample method handler function and COPY FORMAT
handler function use "(internal)" as arguments.

I think that tablesample method names and COPY FORMAT names
will not be conflicted but the limitation (using the same
namespace for tablesample method and COPY FORMAT) is
unnecessary limitation.

How about using prefix ("copy_to_${copy_format_name}" or
something) or suffix ("${copy_format_name}_copy_to" or
something) for function names? For example,
"copy_to_json"/"copy_from_json" for "json" COPY FORMAT.

("copy_${copy_format_name}" that returns copy_handler
encapsulating either copy_to/from_handler depending on the
argument may be an option.)


Thanks,
-- 
kou