[Fixed] `ensureNotNull` exists as an extension fun...

# arrow

[Stylianos Gakis]

[Fixed] ensureNotNull exists as an extension function on EffectScope

Hm I tried to use the ensure function public suspend fun ensure(condition: Boolean, shift: () -> R) inside the EffectScope scope today and I was missing the nice functionality of the kotlin require function which by using a contract allows the compiler to auto-infer the type after that function. Specifically when doing a require not null check in my case.
Since the ensure function does not do that, is there some other API I’m missing which could help me out, or should I just do !! since I know myself at that point that the item is not null?

[Stylianos Gakis]

Ah this exists

@OptIn(ExperimentalContracts::class)
public suspend fun <R, B : Any> EffectScope<R>.ensureNotNull(value: B?, shift: () -> R): B {
  contract { returns() implies (value != null) }
  return value ?: shift(shift())
}

Silly me!

[simon.vergauwen]

It needs to be an extension function because of ExperimentalContracts requiring the fun to be final.

[Youssef Shoaib [MOD]]

Could a B?.ensureNotNull(shift) with the contract and everything exist for Arrow 2.0 with context receivers? It's not a "core" API per se, merely a convenience fun, so could such a fun exist?

[simon.vergauwen]

I'm not sure what you mean at @Youssef Shoaib [MOD]?

context(EffectScope<R>)
public suspend fun <R, B : Any> ensureNotNull(value: B?, shift: () -> R): B {
  contract { returns() implies (value != null) }
  return value ?: shift(shift())
}

[simon.vergauwen]

Having A? as a extension receiver globally is a bad idea, since it's valid for Any?.

[Youssef Shoaib [MOD]]

context(EffectScope<R>)
public suspend fun <R, B : Any> B?.ensureNotNull(shift: () -> R): B {
   contract { returns() implies (value != null) }
   return value ?: shift(shift())
 }

For discoverability. I think it should not pollute the global autocomplete cuz of the context? Maybe IntelliJ would still autocomplete it idk.

[simon.vergauwen]

This function would conflict with for example.
Meaning we cannot make any other extensions for the API name ensureNotNull.

context(EffectScope<R>)
public suspend fun <R, B : Any> Either<R, B?>.ensureNotNull(shift: () -> R): B = TODO

[simon.vergauwen]

For discoverability. I think it should not pollute the global autocomplete cuz of the context?

[Youssef Shoaib [MOD]]

That makes sense yeah. Of course it will take up that name, similar to the Nullable.zip situation. Autocomplete is interesting because I think IntelliJ does show these functions in the global scope then complains about a missing context if you use it, but, I think, it pushes contextual functions (that don't have the required contexts in scope) down the list.

[simon.vergauwen]

In that regard I think the extension function variant would behave better in face of auto-complete, no?