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Date: Thu, 24 Jul 2025 16:10:16 +0200
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Subject: Re: CAST(... ON DEFAULT) - WIP build on top of Error-Safe User
 Functions
To: jian he <jian.universality@gmail.com>
Cc: Corey Huinker <corey.huinker@gmail.com>,
 Isaac Morland <isaac.morland@gmail.com>, pgsql-hackers@lists.postgresql.org
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From: Vik Fearing <vik@postgresfriends.org>
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On 24/07/2025 03:22, jian he wrote:
> +SELECT CAST('a' as int DEFAULT sum(1) ON CONVERSION ERROR); --error
> +SELECT CAST('a' as int DEFAULT sum(1) over() ON CONVERSION ERROR); --error


This seems like an arbitrary restriction.  Can you explain why this is 
necessary?  Those same expressions are allowed as the <cast operand>.


> +SELECT CAST('a' as int DEFAULT ret_setint() ON CONVERSION ERROR) --error
> (ret_setint function is warped as (select 1 union all select 2))


This makes sense to me.


> for array coerce, which you already mentioned, i think the following
> is what we expected.
> +SELECT CAST('{234,def,567}'::text[] AS integer[] DEFAULT '{-1011}' ON
> CONVERSION ERROR);
> +  int4
> +---------
> + {-1011}
> +(1 row)


Yes, that looks correct to me.


> I didn't implement the [ FORMAT <cast template> ] part for now.


That is fine, since it's separate feature


> please check the attached regress test and tests expected result.


Except for the weird restriction on the default value, this all looks 
good to me (with the usual caveat that I am not an expert in C).


Are you planning to also implement the <castable predicate>?

-- 

Vik Fearing

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    <p><br>
    </p>
    <div class="moz-cite-prefix">On 24/07/2025 03:22, jian he wrote:<span
      style="white-space: pre-wrap">
</span></div>
    <blockquote type="cite"
cite="mid:CACJufxFy+DFpJ2e-czyCTAgSJXNFaQGWFKA4mjbW-LAMGc1YBA@mail.gmail.com">
      <pre wrap="" class="moz-quote-pre">+SELECT CAST('a' as int DEFAULT sum(1) ON CONVERSION ERROR); --error
+SELECT CAST('a' as int DEFAULT sum(1) over() ON CONVERSION ERROR); --error
</pre>
    </blockquote>
    <p><br>
    </p>
    <p>This seems like an arbitrary restriction.  Can you explain why
      this is necessary?  Those same expressions are allowed as the
      &lt;cast operand&gt;.</p>
    <p><br>
    </p>
    <blockquote type="cite"
cite="mid:CACJufxFy+DFpJ2e-czyCTAgSJXNFaQGWFKA4mjbW-LAMGc1YBA@mail.gmail.com">
      <pre wrap="" class="moz-quote-pre">+SELECT CAST('a' as int DEFAULT ret_setint() ON CONVERSION ERROR) --error
(ret_setint function is warped as (select 1 union all select 2))</pre>
    </blockquote>
    <p><br>
    </p>
    <p>This makes sense to me.</p>
    <p><br>
    </p>
    <blockquote type="cite"
cite="mid:CACJufxFy+DFpJ2e-czyCTAgSJXNFaQGWFKA4mjbW-LAMGc1YBA@mail.gmail.com">
      <pre wrap="" class="moz-quote-pre">for array coerce, which you already mentioned, i think the following
is what we expected.
+SELECT CAST('{234,def,567}'::text[] AS integer[] DEFAULT '{-1011}' ON
CONVERSION ERROR);
+  int4
+---------
+ {-1011}
+(1 row)</pre>
    </blockquote>
    <p><br>
    </p>
    <p>Yes, that looks correct to me.</p>
    <p><br>
    </p>
    <blockquote type="cite"
cite="mid:CACJufxFy+DFpJ2e-czyCTAgSJXNFaQGWFKA4mjbW-LAMGc1YBA@mail.gmail.com">
      <pre wrap="" class="moz-quote-pre">I didn't implement the [ FORMAT &lt;cast template&gt; ] part for now.</pre>
    </blockquote>
    <p><br>
    </p>
    <p>That is fine, since it's separate feature</p>
    <p><br>
    </p>
    <blockquote type="cite"
cite="mid:CACJufxFy+DFpJ2e-czyCTAgSJXNFaQGWFKA4mjbW-LAMGc1YBA@mail.gmail.com">
      <pre wrap="" class="moz-quote-pre">please check the attached regress test and tests expected result.
</pre>
    </blockquote>
    <p><br>
    </p>
    <p>Except for the weird restriction on the default value, this all
      looks good to me (with the usual caveat that I am not an expert in
      C).</p>
    <p><br>
    </p>
    <p>Are you planning to also implement the &lt;castable
      predicate&gt;?</p>
    <p>-- </p>
    <p>Vik Fearing</p>
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