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d

dumptruckman

03/26/2020, 8:36 PM
From what I remember, the use of the double bang is discouraged. However, I find myself using it a lot to intentionally throw an NPE when something really shouldn’t be null. Example would be a SQL query that should either return no rows or a row with a single column with a non null value. There’s no reason the column should ever be null unless someone changed the DDL of the table at which point the NPE essentially just informs them they have more work to do with such a change. Anyone else experiencing this?
t

tddmonkey

03/26/2020, 8:38 PM
In those cases I prefer a
?: error("some useful information about why it failed")
1
s

Shawn

03/26/2020, 8:38 PM
colin beat me to it
an NPE doesn’t intrinsically tell you anything more specific than “you’re trying to dereference a null pointer dummy”
calling
error()
with a useful message is way more helpful (and easier to search for in the codebase)
d

dumptruckman

03/26/2020, 8:42 PM
Yeah, I guess that’s true.
t

tddmonkey

03/26/2020, 8:43 PM
The only time I’ll use
!!
is when it absolutely cannot be null but I’m interoping with something that doesn’t let the compiler know
d

dumptruckman

03/26/2020, 8:51 PM
I guess a lot of these use cases are the result of an inline function I created to make getting values from a ResultSet easier. Example:
val timestamp: LocalDate = rs["create_date"]!!
though usually the type inference comes from a method/constructor parameter
but I think I just realized that maybe I wrote that function incorrectly…
s

Shawn

03/26/2020, 8:54 PM
mazel tov 🎉
d

dumptruckman

03/26/2020, 8:54 PM
inline operator fun <reified T> ResultSet.get(columnLabel: CharSequence): T? = getObject(columnLabel.toString(), T::class.java)
return type should probably just be
T
right?
s

Shawn

03/26/2020, 8:55 PM
that makes sense, assuming you’re intending for folks to parameterize the call properly if the field is intentionally nullable
d

dumptruckman

03/26/2020, 8:55 PM
right
Actually, I think there was something peculiar that required that due to the way getObject handles primitives…
Or the interop when inferring types from java primitives.
yeah.. so you could infer from an
int
and easily use
rs["id"] ?: 0
SO… having remembered that, it kind of forces me to use !! to get non-nullable types out of it. I feel like putting ?: error(“…”) after each call to it would quickly get unsightly.
Message(
    rs["create_date"] ?: error("create_date is null"),
    rs["body"] ?: error("body is null"),
    rs["subject"],
    rs["message_id"] ?: error("message_id is null")
)
Would you still prefer an elvis error in this case?
s

Shawn

03/26/2020, 9:07 PM
feel like you could define a different getter if you’re not super attached to the operator fun
d

dumptruckman

03/26/2020, 9:07 PM
Specifically for the cases with numbers?
s

Shawn

03/26/2020, 9:08 PM
well idk about the types in question here but you could maybe have a
get()
and a
getNullable()
or a
getThrowing()
if you actually want that to be the exceptional behavior
your call
d

dumptruckman

03/26/2020, 9:10 PM
The operator part of it was pretty nice I think.
Message(
    rs["create_date"]!!,
    rs["body"]!!,
    rs["subject"],
    rs["message_id"]!!
)
s

Shawn

03/26/2020, 9:12 PM
Message(
  rs["create_date"],  // these will throw
  rs["body"],
  rs.getNullable("subject"),  // this will not
  rs["message_id"]
)
it’s perhaps not as nice-looking but is probably easier to debug
ultimately it’s up to you what kind of API you wanna publish
I see where you’re coming from and don’t necessarily disagree
d

dumptruckman

03/26/2020, 9:13 PM
I could abuse the
invoke
operator for the other case… but that’s probably not a good idea.
s

Shawn

03/26/2020, 9:14 PM
it’s not great, would probably surprise folks (though the scala people might not hate it lol)
d

dumptruckman

03/26/2020, 9:15 PM
Maybe I could just create an extra extension function for the ones that have exceptional cases… I’ll have to fiddle around with that.
rs["id"] { 0 }
overload get with a block param
Less intuitive though I think
s

Shawn

03/26/2020, 9:23 PM
idk, providing a default is pretty different from NPEing if you’ve reached an illegal state
d

dumptruckman

03/26/2020, 9:23 PM
You know… to be fair, if that function didn’t return
T?
it would still NPE if the result of
getObject
ended up being null
Which would occur if the programmer made a mistake or if the DDL changed.
s

sindrenm

03/27/2020, 9:26 AM
As an alternative to the
?: error("message")
approach, there's also
checkNotNull
and
requireNotNull
, which might be of interest. I tend to favor those over
!!
, at least, and usually also
checkNotNull(foo) { "message" }
over
foo ?: error("message")
.
t

tddmonkey

03/27/2020, 9:59 AM
For things like this we have an extension method to make things clearer, so something like:
Message(
    rs["create_date"].orDie(),
    rs["body"].orDie(),
    rs["subject"],
    rs["message_id"].orDie()
)
m

Mike

03/27/2020, 1:02 PM
Although not pretty, I prefer
checkNull
or
requireNull
calls. And function returns non-null. More explicit than !!, and throws
Illegal
exception rather than NPE. I find that more realistic, as
!!
should only be used in cases where the compiler can't figure it out, but you KNOW it can't/won't be null at that point.