From what I remember the use of the double bang is discourag

Question

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

tddmonkey · Answer

In those cases I prefer a ` error some useful information about why it failed `

Shawn · Answer

colin beat me to it

Shawn · Answer

an NPE doesn t intrinsically tell you anything more specific than you re trying to dereference a null pointer dummy

Shawn · Answer

calling `error ` with a useful message is way more helpful and easier to search for in the codebase

dumptruckman · Answer

Yeah I guess that s true

tddmonkey · Answer

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

dumptruckman · Answer

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 `

dumptruckman · Answer

though usually the type inference comes from a method constructor parameter

dumptruckman · Answer

but I think I just realized that maybe I wrote that function incorrectly

Shawn · Answer

mazel tov tada

dumptruckman · Answer

```inline operator fun lt reified T gt ResultSet get columnLabel CharSequence T = getObject columnLabel toString T class java ```

dumptruckman · Answer

return type should probably just be `T` right

Shawn · Answer

that makes sense assuming you re intending for folks to parameterize the call properly if the field is intentionally nullable

dumptruckman · Answer

right

dumptruckman · Answer

Actually I think there was something peculiar that required that due to the way getObject handles primitives

dumptruckman · Answer

Or the interop when inferring types from java primitives

dumptruckman · Answer

yeah so you could infer from an `int` and easily use `rs id 0`

dumptruckman · Answer

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

dumptruckman · Answer

```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 ```

dumptruckman · Answer

Would you still prefer an elvis error in this case

Shawn · Answer

feel like you could define a different getter if you re not super attached to the operator fun

dumptruckman · Answer

Specifically for the cases with numbers

Shawn · Answer

well idk about the types in question here but you could maybe have a `get ` and a `getNullable `

Shawn · Answer

or a `getThrowing ` if you actually want that to be the exceptional behavior

Shawn · Answer

your call

dumptruckman · Answer

The operator part of it was pretty nice I think ```Message rs create date rs body rs subject rs message id ```

Shawn · Answer

```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

Shawn · Answer

ultimately it s up to you what kind of API you wanna publish

Shawn · Answer

I see where you re coming from and don t necessarily disagree

dumptruckman · Answer

I could abuse the `invoke` operator for the other case but that s probably not a good idea

Shawn · Answer

it s not great would probably surprise folks though the scala people might not hate it lol

dumptruckman · Answer

Maybe I could just create an extra extension function for the ones that have exceptional cases I ll have to fiddle around with that

dumptruckman · Answer

`rs id 0 `

dumptruckman · Answer

overload get with a block param

dumptruckman · Answer

Less intuitive though I think

Shawn · Answer

idk providing a default is pretty different from NPEing if you ve reached an illegal state

dumptruckman · Answer

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

dumptruckman · Answer

Which would occur if the programmer made a mistake or if the DDL changed

sindrenm · Answer

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 `

tddmonkey · Answer

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 ```

Mike · Answer

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