What exactly is returned in a Scala Future?
I am new to Scala and am working on an application using akka and futures
I have a class(C) that processes a future and returns a List(L) of objects type X. X has a field y and it is this field I am interesed in. (Note: L was previously converted from a ListBuffer type).
In the Main Class that calls C the code to process the result is:
Snippet A:
result1.onComplete {
result =>
result.foreach(f = (o: List[X]) => {
o.foreach(f = (o: x) => {
println(X.y)
})
})
}
I can also use this code:
Snippet B:
result1 onSuccess{
case result =>
result.foreach(f = (o: X) => {
println(o.y)
})
}
Obviously, as OnSuccess is deprecated the first form may be preferred. The second form (Snippet B) I can understand, but I am baffled as to why, when using onComplete, I have to use nested 'foreach' to get to the same result. If anyone can help as I dont yet have a clear conception of what 'result' (Try[T] => U) ??? actually is. Thanks in advance..:)
scala
edited Nov 26 '18 at 11:11
Jeffrey Chung
14.3k62142
asked Nov 25 '18 at 14:15
Kammo3 Kammo3
113
add a comment |
I am new to Scala and am working on an application using akka and futures
I have a class(C) that processes a future and returns a List(L) of objects type X. X has a field y and it is this field I am interesed in. (Note: L was previously converted from a ListBuffer type).
In the Main Class that calls C the code to process the result is:
Snippet A:
result1.onComplete {
result =>
result.foreach(f = (o: List[X]) => {
o.foreach(f = (o: x) => {
println(X.y)
})
})
}
I can also use this code:
Snippet B:
result1 onSuccess{
case result =>
result.foreach(f = (o: X) => {
println(o.y)
})
}
Obviously, as OnSuccess is deprecated the first form may be preferred. The second form (Snippet B) I can understand, but I am baffled as to why, when using onComplete, I have to use nested 'foreach' to get to the same result. If anyone can help as I dont yet have a clear conception of what 'result' (Try[T] => U) ??? actually is. Thanks in advance..:)
scala
edited Nov 26 '18 at 11:11
Jeffrey Chung
14.3k62142
asked Nov 25 '18 at 14:15
Kammo3 Kammo3
113
1
Could you please clarify your question.
– Chaitanya Waikar
Nov 25 '18 at 14:24
My question boils down to: What is the fundamental difference between onComplete and onSuccess methods that requires the difference in code given above.
– Kammo3
Nov 25 '18 at 14:30
add a comment |
I am new to Scala and am working on an application using akka and futures
I have a class(C) that processes a future and returns a List(L) of objects type X. X has a field y and it is this field I am interesed in. (Note: L was previously converted from a ListBuffer type).
In the Main Class that calls C the code to process the result is:
Snippet A:
result1.onComplete {
result =>
result.foreach(f = (o: List[X]) => {
o.foreach(f = (o: x) => {
println(X.y)
})
})
}
I can also use this code:
Snippet B:
result1 onSuccess{
case result =>
result.foreach(f = (o: X) => {
println(o.y)
})
}
Obviously, as OnSuccess is deprecated the first form may be preferred. The second form (Snippet B) I can understand, but I am baffled as to why, when using onComplete, I have to use nested 'foreach' to get to the same result. If anyone can help as I dont yet have a clear conception of what 'result' (Try[T] => U) ??? actually is. Thanks in advance..:)
scala
edited Nov 26 '18 at 11:11
Jeffrey Chung
14.3k62142
asked Nov 25 '18 at 14:15
Kammo3 Kammo3
113
I am new to Scala and am working on an application using akka and futures
I have a class(C) that processes a future and returns a List(L) of objects type X. X has a field y and it is this field I am interesed in. (Note: L was previously converted from a ListBuffer type).
In the Main Class that calls C the code to process the result is:
Snippet A:
result1.onComplete {
result =>
result.foreach(f = (o: List[X]) => {
o.foreach(f = (o: x) => {
println(X.y)
})
})
}
I can also use this code:
Snippet B:
result1 onSuccess{
case result =>
result.foreach(f = (o: X) => {
println(o.y)
})
}
Obviously, as OnSuccess is deprecated the first form may be preferred. The second form (Snippet B) I can understand, but I am baffled as to why, when using onComplete, I have to use nested 'foreach' to get to the same result. If anyone can help as I dont yet have a clear conception of what 'result' (Try[T] => U) ??? actually is. Thanks in advance..:)
scala
scala
edited Nov 26 '18 at 11:11
Jeffrey Chung
14.3k62142
asked Nov 25 '18 at 14:15
Kammo3 Kammo3
113
edited Nov 26 '18 at 11:11
Jeffrey Chung
14.3k62142
asked Nov 25 '18 at 14:15
Kammo3 Kammo3
113
edited Nov 26 '18 at 11:11
Jeffrey Chung
14.3k62142
edited Nov 26 '18 at 11:11
Jeffrey Chung
14.3k62142
edited Nov 26 '18 at 11:11
Jeffrey Chung
14.3k62142
14.3k62142
asked Nov 25 '18 at 14:15
Kammo3 Kammo3
113
asked Nov 25 '18 at 14:15
Kammo3 Kammo3
113
asked Nov 25 '18 at 14:15
Kammo3 Kammo3
113
113
1
Could you please clarify your question.
– Chaitanya Waikar
Nov 25 '18 at 14:24
My question boils down to: What is the fundamental difference between onComplete and onSuccess methods that requires the difference in code given above.
– Kammo3
Nov 25 '18 at 14:30
add a comment |
1
Could you please clarify your question.
– Chaitanya Waikar
Nov 25 '18 at 14:24
My question boils down to: What is the fundamental difference between onComplete and onSuccess methods that requires the difference in code given above.
– Kammo3
Nov 25 '18 at 14:30
1
1
Could you please clarify your question.
– Chaitanya Waikar
Nov 25 '18 at 14:24
Could you please clarify your question.
– Chaitanya Waikar
Nov 25 '18 at 14:24
My question boils down to: What is the fundamental difference between onComplete and onSuccess methods that requires the difference in code given above.
– Kammo3
Nov 25 '18 at 14:30
My question boils down to: What is the fundamental difference between onComplete and onSuccess methods that requires the difference in code given above.
– Kammo3
Nov 25 '18 at 14:30
add a comment |
1 Answer
1
active
oldest
votes
If you take a look to the Future.onComplete scaladoc, you will see that it receives a function from Try[T], (where T is the type of your future), to Unit.
"When this future is completed, either through an exception, or a value, apply the provided function".
"Note that the returned value of f will be discarded".
The Try is there to catch failures on the asynchronous computation - that's why you need the two foreach, the first one is to extract the Successful List from the Try, and the second one is to extract each element O from the List.
You didn't need two in the case of onSuccess because, as the name says that callback would only be called if the Future completed successfully.
However, note that doing a foreach on a Try is a bad idea, since you are not handling the failure, also the code become hard to read - try this instead.
import scala.concurrent.Future
import scala.concurrent.ExecutionContext.Implicits.global
import scala.util.{Success, Failure}
case class Result(data: Int)
val process: Future[List[Result]] =
Future.successful(List(Result(data = 5), Result(data = 3)))
process.onComplete {
case Success(results) =>
for (result <- results) {
println(result.data)
}
case Failure(ex) =>
println(s"Error: ${ex.getMessage}")
}
answered Nov 25 '18 at 14:38
Luis Miguel Mejía SuárezLuis Miguel Mejía Suárez
2,7472923
add a comment |
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If you take a look to the Future.onComplete scaladoc, you will see that it receives a function from Try[T], (where T is the type of your future), to Unit.
"When this future is completed, either through an exception, or a value, apply the provided function".
"Note that the returned value of f will be discarded".
The Try is there to catch failures on the asynchronous computation - that's why you need the two foreach, the first one is to extract the Successful List from the Try, and the second one is to extract each element O from the List.
You didn't need two in the case of onSuccess because, as the name says that callback would only be called if the Future completed successfully.
However, note that doing a foreach on a Try is a bad idea, since you are not handling the failure, also the code become hard to read - try this instead.
import scala.concurrent.Future
import scala.concurrent.ExecutionContext.Implicits.global
import scala.util.{Success, Failure}
case class Result(data: Int)
val process: Future[List[Result]] =
Future.successful(List(Result(data = 5), Result(data = 3)))
process.onComplete {
case Success(results) =>
for (result <- results) {
println(result.data)
}
case Failure(ex) =>
println(s"Error: ${ex.getMessage}")
}
answered Nov 25 '18 at 14:38
Luis Miguel Mejía SuárezLuis Miguel Mejía Suárez
2,7472923
add a comment |
If you take a look to the Future.onComplete scaladoc, you will see that it receives a function from Try[T], (where T is the type of your future), to Unit.
"When this future is completed, either through an exception, or a value, apply the provided function".
"Note that the returned value of f will be discarded".
The Try is there to catch failures on the asynchronous computation - that's why you need the two foreach, the first one is to extract the Successful List from the Try, and the second one is to extract each element O from the List.
You didn't need two in the case of onSuccess because, as the name says that callback would only be called if the Future completed successfully.
However, note that doing a foreach on a Try is a bad idea, since you are not handling the failure, also the code become hard to read - try this instead.
import scala.concurrent.Future
import scala.concurrent.ExecutionContext.Implicits.global
import scala.util.{Success, Failure}
case class Result(data: Int)
val process: Future[List[Result]] =
Future.successful(List(Result(data = 5), Result(data = 3)))
process.onComplete {
case Success(results) =>
for (result <- results) {
println(result.data)
}
case Failure(ex) =>
println(s"Error: ${ex.getMessage}")
}
answered Nov 25 '18 at 14:38
Luis Miguel Mejía SuárezLuis Miguel Mejía Suárez
2,7472923
add a comment |
If you take a look to the Future.onComplete scaladoc, you will see that it receives a function from Try[T], (where T is the type of your future), to Unit.
"When this future is completed, either through an exception, or a value, apply the provided function".
"Note that the returned value of f will be discarded".
The Try is there to catch failures on the asynchronous computation - that's why you need the two foreach, the first one is to extract the Successful List from the Try, and the second one is to extract each element O from the List.
You didn't need two in the case of onSuccess because, as the name says that callback would only be called if the Future completed successfully.
However, note that doing a foreach on a Try is a bad idea, since you are not handling the failure, also the code become hard to read - try this instead.
import scala.concurrent.Future
import scala.concurrent.ExecutionContext.Implicits.global
import scala.util.{Success, Failure}
case class Result(data: Int)
val process: Future[List[Result]] =
Future.successful(List(Result(data = 5), Result(data = 3)))
process.onComplete {
case Success(results) =>
for (result <- results) {
println(result.data)
}
case Failure(ex) =>
println(s"Error: ${ex.getMessage}")
}
answered Nov 25 '18 at 14:38
Luis Miguel Mejía SuárezLuis Miguel Mejía Suárez
2,7472923
If you take a look to the Future.onComplete scaladoc, you will see that it receives a function from Try[T], (where T is the type of your future), to Unit.
"When this future is completed, either through an exception, or a value, apply the provided function".
"Note that the returned value of f will be discarded".
The Try is there to catch failures on the asynchronous computation - that's why you need the two foreach, the first one is to extract the Successful List from the Try, and the second one is to extract each element O from the List.
You didn't need two in the case of onSuccess because, as the name says that callback would only be called if the Future completed successfully.
However, note that doing a foreach on a Try is a bad idea, since you are not handling the failure, also the code become hard to read - try this instead.
import scala.concurrent.Future
import scala.concurrent.ExecutionContext.Implicits.global
import scala.util.{Success, Failure}
case class Result(data: Int)
val process: Future[List[Result]] =
Future.successful(List(Result(data = 5), Result(data = 3)))
process.onComplete {
case Success(results) =>
for (result <- results) {
println(result.data)
}
case Failure(ex) =>
println(s"Error: ${ex.getMessage}")
}
answered Nov 25 '18 at 14:38
Luis Miguel Mejía SuárezLuis Miguel Mejía Suárez
2,7472923
edited Nov 25 '18 at 15:19
answered Nov 25 '18 at 14:38
Luis Miguel Mejía SuárezLuis Miguel Mejía Suárez
2,7472923
answered Nov 25 '18 at 14:38
Luis Miguel Mejía SuárezLuis Miguel Mejía Suárez
2,7472923
answered Nov 25 '18 at 14:38
Luis Miguel Mejía SuárezLuis Miguel Mejía Suárez
2,7472923
2,7472923
add a comment |
add a comment |
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1
Could you please clarify your question.
– Chaitanya Waikar
Nov 25 '18 at 14:24
My question boils down to: What is the fundamental difference between onComplete and onSuccess methods that requires the difference in code given above.
– Kammo3
Nov 25 '18 at 14:30