generics vs. checked exceptions

[John Hendrikx]

On 16/03/2022 18:36, John Rose wrote:
> All that said, I don’t want to work on it now, because I have far more 
> pressing things to get done: pressing in a good, exciting, and 
> fruitful way.  I imagine Brian has similar feelings.
>
> (Idle question:  Does fruitful pressing eventually lead to good 
> vintages?  One hopes!)
>
> — John
>
> P.S. On one of my many back burners, I’ve been experimenting with 
> exposing checked exceptions through Java’s *existing* generics 
> (nothing new) to find the limits of what they can do.  Here’s a 
> snapshot, FWIW, of small number of types which expose not only the 
> possible normal result value of an expression, but also its possible 
> exceptional result:
>
> http://cr.openjdk.java.net/~jrose/draft/exbox-javadoc

I've been playing with something similar :)

Here is an implementation of Streams which allows checked exceptions 
(upto 3) with standard Java:

https://github.com/hjohn/MediaSystem-v2/tree/master/mediasystem-util/src/main/java/hs/mediasystem/util/checked

The test case has readable examples:

https://github.com/hjohn/MediaSystem-v2/blob/master/mediasystem-util/src/test/java/hs/mediasystem/util/checked/CheckedStreamsTest.java

The exceptions are (re)thrown and declared by the terminal operations of 
Stream.  The lack of a generic type parameter that can indicate a set of 
exceptions makes it a bit cumbersome, but it does not cause any problems 
when no exceptions are thrown or only runtime exceptions are thrown.  In 
fact, surprisingly, declaring the same checked exception (through a 
generic parameter) several times is seemingly allowed without problem.

--John