Thread: Implicit type conversion -- where documented?

Hi,

On Thu, Nov 10, 2022 at 06:27:21PM -0800, Kirk Parker wrote:
> I came across what seems like anomalous behavior regarding
> implicit conversion from a numeric type to text.  You can write:
>
>     select 3.1416 || '?';
>
> and the number implicitly converts to text and concatenates just fine, but
> writing:
>
>    select trim(3.1416);
>
> fails with an error message.  This seems odd to me--in both cases a float
> literal is used in a context expecting text; in one case it implicitly
> converts, in the other it doesn't.
>
> *This brings up my real question*: are the details of this documented
> anywhere?  Chapter 10 refers to ' implicit conversions' but I can't see
> anywhere that the docs explain the details of how it is done, that would
> explain the observed difference in behavior described above.

There are actually no cast defined from numeric to text, so you won't find a
documentation for that.

The first example is working as documented at
https://www.postgresql.org/docs/current/functions-string.html:

anynonarray || text → text
Converts the non-string input to text, then concatenates the two strings. (The
non-string input cannot be of an array type, because that would create
ambiguity with the array || operators. If you want to concatenate an array's
text equivalent, cast it to text explicitly.)