Re: [PATCH][PROPOSAL] Add enum releation option type

From: Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>
To: Nikolay Shaplov <dhyan(at)nataraj(dot)su>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: [PATCH][PROPOSAL] Add enum releation option type
Date: 2018-02-09 21:45:29
Message-ID: 20180209214529.mbz6iqji7v436xde@alvherre.pgsql
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Nikolay Shaplov wrote:

> I found out, that all relation options of string type in current postgres, are
> actually behaving as "enum" type.

If this patch gets in, I wonder if there are any external modules that
use actual strings. An hypothetical example would be something like a
SSL cipher list; it needs to be somewhat free-form that an enum would
not cut it. If there are such modules, then even if we remove all
existing in-core use cases we should keep the support code for strings.
Maybe we need some in-core user to verify the string case still works.
A new module in src/test/modules perhaps? On the other hand, if we can
find no use for these string reloptions, maybe we should just remove the
support, since as I recall it's messy enough.

> [...] But each time this behavior is implemented as validate function
> plus strcmp to compare option value against one of the possible
> values.
>
> I think it is not the best practice. It is better to have enum type
> where it is technically enum, and keep sting type for further usage
> (for example for some kind of index patterns or something like this).

Agreed with the goal, for code simplicity and hopefully reducing
code duplication.

> Possible flaws:
>
> 1. I've changed error message from 'Valid values are "XXX", "YYY" and "ZZZ".'
> to 'Valid values are "XXX", "YYY", "ZZZ".' to make a code a bit simpler. If it
> is not acceptable, please let me know, I will add "and" to the string.

I don't think we care about this, but is this still the case if you use
a stringinfo?

> 2. Also about the string with the list of acceptable values: the code that
> creates this string is inside parse_one_reloption function now.

I think you could save most of that mess by using appendStringInfo and
friends.

I don't much like the way you've represented the list of possible values
for each enum. I think it'd be better to have a struct that represents
everything about each value (string name and C symbol. Maybe the
numerical value too if that's needed, but is it? I suppose all code
should use the C symbol only, so why do we care about the numerical
value?).

--
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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