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In-Reply-To: 
 <CADkLM=f0xruKRH+6XvCsM1EVic9y4BL4AFo3VUfvRLdu-Qp5Gg@mail.gmail.com>
From: Corey Huinker <corey.huinker@gmail.com>
Date: Tue, 10 Mar 2026 12:22:25 -0400
Message-ID: 
 <CADkLM=e4y2bLv-6_JY5c6vC9QtweW9VfxVmVJFpcriy8Rs23TA@mail.gmail.com>
Subject: Re: CAST(... ON DEFAULT) - WIP build on top of Error-Safe User
 Functions
To: jian he <jian.universality@gmail.com>
Cc: Amul Sul <sulamul@gmail.com>, Kirill Reshke <reshkekirill@gmail.com>,
	Vik Fearing <vik@postgresfriends.org>,
 Isaac Morland <isaac.morland@gmail.com>,
	pgsql-hackers@lists.postgresql.org
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On Wed, Jan 14, 2026 at 5:16=E2=80=AFPM Corey Huinker <corey.huinker@gmail.=
com>
wrote:

> > +               /*
>> > +                * Here, we cannot deparsing cast_expr directly, since
>> > +                * transformTypeSafeCast may have folded it into a
>> simple
>> > +                * constant or NULL. Instead, we use source_expr and
>> > +                * default_expr to reconstruct the CAST DEFAULT clause=
.
>> > +                */
>> >
>> > I am wondering how other places handle expression deparsing; do they
>> > hold the original expression along with the transformed expression?
>>
>
> In my initial implementation of this, I modified CoalesceExpr to ensure
> that the default clause was evaluated if and only if the initial expressi=
on
> failed.
>
>
>
>> rebased, many variable names have been renamed, comments adjusted.
>
>
> The new SAFE option on user defined cast functions looks good to me.
>
> I am concerned that adding _safe overhead to all cast functions will be
> received poorly, but if it is poorly received then reverting isn't that
> hard.
>
> I'm going to re-review the whole patch set, but I wanted to say that I
> like the main points of the changes so far.
>

I picked this back up again, pondered adding the IS CASTABLE AS syntax to
the patch, but ultimately decided that it should be a separate patch.

While I still think the patch order is a bit backwards [1], the order
chosen does have a sense to it, and whether or not that is the right order
is up to the committer. Please post a rebase so I can mark it as ready for
committer.


[1] I would have preferred adding the CAST functionality first, then
switching over each datatype one-by-one, thus demonstrating that non-safe
datatypes can co-exist with this new functionality. But that's just my
personal preference.

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<div dir=3D"ltr"><div class=3D"gmail_quote gmail_quote_container"><div dir=
=3D"ltr" class=3D"gmail_attr">On Wed, Jan 14, 2026 at 5:16=E2=80=AFPM Corey=
 Huinker &lt;<a href=3D"mailto:corey.huinker@gmail.com">corey.huinker@gmail=
.com</a>&gt; wrote:<br></div><blockquote class=3D"gmail_quote" style=3D"mar=
gin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1=
ex"><div dir=3D"ltr"><div class=3D"gmail_quote"><blockquote class=3D"gmail_=
quote" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,=
204);padding-left:1ex">
&gt; +=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0/*<br>
&gt; +=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 * Here, we ca=
nnot deparsing cast_expr directly, since<br>
&gt; +=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 * transformTy=
peSafeCast may have folded it into a simple<br>
&gt; +=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 * constant or=
 NULL. Instead, we use source_expr and<br>
&gt; +=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 * default_exp=
r to reconstruct the CAST DEFAULT clause.<br>
&gt; +=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 */<br>
&gt;<br>
&gt; I am wondering how other places handle expression deparsing; do they<b=
r>
&gt; hold the original expression along with the transformed expression?<br=
></blockquote><div><br></div><div>In my initial implementation of this, I m=
odified CoalesceExpr to ensure that the default clause was evaluated if and=
 only if the initial expression failed.</div><div></div><div><br></div><div=
>=C2=A0</div><blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px =
0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
rebased, many variable names have been renamed, comments adjusted.</blockqu=
ote><div><br></div><div>The new SAFE option on user defined cast functions =
looks good to me.<br><br>I am concerned that adding _safe overhead to all c=
ast functions will be received poorly, but if it is poorly received then re=
verting isn&#39;t that hard.</div><div><br></div><div>I&#39;m going to re-r=
eview the whole patch set, but I wanted to say that I like the main points =
of the changes so far.</div></div></div></blockquote><div><br></div><div>I =
picked this back up again, pondered adding the IS CASTABLE AS syntax to the=
 patch, but ultimately decided that it should be a separate patch.<br><br><=
/div><div>While I still think the patch order is a bit backwards [1], the o=
rder chosen does have a sense to it, and whether or not that is the right o=
rder is up to the committer. Please post a rebase so I can mark it as ready=
 for committer.<br><br><br></div><div>[1] I would have preferred adding the=
 CAST functionality first, then switching over each datatype one-by-one, th=
us demonstrating that non-safe datatypes can co-exist with this new functio=
nality. But that&#39;s just my personal preference.</div></div></div>

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