update: ZIO#head to use subtype of Seq, not List #9502
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| * non-empty or fails with the error `None` if the list is empty. | ||
| */ | ||
| final def head[B](implicit ev: A IsSubtypeOfOutput List[B], trace: Trace): ZIO[R, Option[E], B] = | ||
| final def head[B](implicit ev: A IsSubtypeOfOutput Seq[B], trace: Trace): ZIO[R, Option[E], B] = |
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Btw it doesn't impact binary compatibility?
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Pretty sure it's okay. We can introduce a private method if you think it's a concern. The bytecode looks like this:
default public <B> ZIO<R, Option<E>, B> head(IsSubtypeOfOutput<A, Seq<B>> ev, Object trace) {
return this.foldZIO((Function1<Object, Exit> & Serializable)e -> Exit$.MODULE$.fail(new Some<Object>(e)), (Function1<Object, ZIO> & Serializable)a -> ((IterableOps)ev.apply(a)).headOption().fold((Function0<Exit> & Serializable)() -> Exit$.MODULE$.failNone(), ZIO$.MODULE$.successFn()), CanFail$.MODULE$.canFail(), trace);
}
The IsSubtypeOf<A, Seq<B>> will be erased, so it shouldn't matter ... which would be problematic if this required changing the body of the function.
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The evidence is purely to make the compiler happy as well. headOption exists on the Seq interface, which the JVM will traverse available interfaces to find the method to dispatch to anyways.
The evidence provided is non-important (type wise) as it's essentially just identity:
https://github.com/zio/zio/blob/series/2.x/core/shared/src/main/scala/zio/IsSubtype.scala#L11
https://github.com/scala/scala/blob/c6ce350a8e231351256280b0fae9a85bba0fdfbc/src/library/scala/typeConstraints.scala#L152
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Yeah this should be binary compatible as @hearnadam mentioned due to erasure
Closes #4315