Proposal: is_castable

Currently there is no way to check if CAST will succeed.

Therefore I propose adding new function: is_castable

SELECT is_castable('foo' as time) // false
SELECT is_castable('123' as numeric) // true
SELECT is_castable(1.5 as int) // true
SELECT is_castable('1.5' as int) // false

Many users write their own functions:

https://stackoverflow.com/q/10306830/2446102 (11k views, ~25 upvotes)
https://stackoverflow.com/q/36775814/2446102
https://stackoverflow.com/a/16206123/2446102 (72k views, 70 upvotes)
https://stackoverflow.com/q/2082686/2446102 (174k views, ~150 upvotes)

Similar features are implemented in:
- SQL Server (as TRY_CONVERT)
- Oracle (as CONVERT([val] DEFAULT [expr] ON CONVERSION ERROR)

I would love to implement it myself, but my knowledge of C is superficial.

Thanks,
Michał Wadas