Suggestion: optionally return default value instead of error on failed cast

Hi,

currently a failed cast throws an error. It would be useful to have a 
way to get a default value instead.

T-SQL has try_cast [1]
Oracle has CAST(... AS .. DEFAULT ... ON CONVERSION ERROR) [2]

The DEFAULT ... ON CONVERSION ERROR syntax seems like it could be 
implemented in PostgreSQL. Even if only DEFAULT NULL was supported (at 
first) that would already help.

The short syntax could be extended for the DEFAULT NULL case, too:

SELECT '...'::type -- throws error
SELECT '...':::type -- returns NULL

I couldn't find any previous discussion on this, please advise in case I 
just missed it.

Thoughts?

Best

Wolfgang

[1]: 
https://docs.microsoft.com/en-us/sql/t-sql/functions/try-cast-transact-sql
[2]: 
https://docs.oracle.com/en/database/oracle/oracle-database/12.2/sqlrf/CAST.html