Mixing
Understanding Scala default argument message
I am playing around with some Scala code and have met with an error message I don't quite follow. Below is my code
val ignoredIds = Array("one", "two", "three")
def csNotify(x : Any): String = {
case org: String if !ignoredIds.contains(x) =>
println( s" $x should not be here")
"one"
case org : String if ignoredIds.contains(x) =>
println(s"$x should be here")
"two"
}
csNotify("four")
The console output is that I am the arguments for a default function must be known. The error point appears to be pointing at the " String = ". Why would this be the case ? The function should check the two cases and return a string ?
scala methods
asked Nov 22 '18 at 11:19
SteveSteve
1,65021217
add a comment |
I am playing around with some Scala code and have met with an error message I don't quite follow. Below is my code
val ignoredIds = Array("one", "two", "three")
def csNotify(x : Any): String = {
case org: String if !ignoredIds.contains(x) =>
println( s" $x should not be here")
"one"
case org : String if ignoredIds.contains(x) =>
println(s"$x should be here")
"two"
}
csNotify("four")
The console output is that I am the arguments for a default function must be known. The error point appears to be pointing at the " String = ". Why would this be the case ? The function should check the two cases and return a string ?
scala methods
asked Nov 22 '18 at 11:19
SteveSteve
1,65021217
add a comment |
I am playing around with some Scala code and have met with an error message I don't quite follow. Below is my code
val ignoredIds = Array("one", "two", "three")
def csNotify(x : Any): String = {
case org: String if !ignoredIds.contains(x) =>
println( s" $x should not be here")
"one"
case org : String if ignoredIds.contains(x) =>
println(s"$x should be here")
"two"
}
csNotify("four")
The console output is that I am the arguments for a default function must be known. The error point appears to be pointing at the " String = ". Why would this be the case ? The function should check the two cases and return a string ?
scala methods
asked Nov 22 '18 at 11:19
SteveSteve
1,65021217
I am playing around with some Scala code and have met with an error message I don't quite follow. Below is my code
val ignoredIds = Array("one", "two", "three")
def csNotify(x : Any): String = {
case org: String if !ignoredIds.contains(x) =>
println( s" $x should not be here")
"one"
case org : String if ignoredIds.contains(x) =>
println(s"$x should be here")
"two"
}
csNotify("four")
The console output is that I am the arguments for a default function must be known. The error point appears to be pointing at the " String = ". Why would this be the case ? The function should check the two cases and return a string ?
scala methods
scala methods
asked Nov 22 '18 at 11:19
SteveSteve
1,65021217
asked Nov 22 '18 at 11:19
SteveSteve
1,65021217
asked Nov 22 '18 at 11:19
SteveSteve
1,65021217
asked Nov 22 '18 at 11:19
SteveSteve
1,65021217
asked Nov 22 '18 at 11:19
SteveSteve
1,65021217
1,65021217
add a comment |
add a comment |
3 Answers
3
active
oldest
votes
Your case is not finding the match against which it can check your block , and you have missed the match block:
val ignoredIds = Array("one", "two", "three")
def csNotify(x : Any): String = x match {
case org: String if !ignoredIds.contains(x) =>
println( s" $x should not be here")
"one"
case org : String if ignoredIds.contains(x) =>
println(s"$x should be here")
"two"
}
csNotify("four")
So basically when you pass x in method , you have to give it for match as well.
answered Nov 22 '18 at 11:27
Amit PrasadAmit Prasad
573315
add a comment |
Amit Prasad's answer already shows how to fix it, but to explain the error message:
{
case org: String if !ignoredIds.contains(x) =>
println( s" $x should not be here")
"one"
case org : String if ignoredIds.contains(x) =>
println(s"$x should be here")
"two"
}
on its own (without ... match before it) is a pattern-matching anonymous function, which can only be used where the compiler knows the argument type from the context, i.e. the expected type must be either PartialFunction[Something, SomethingElse] or a single-abstract-method type (including Something => SomethingElse).
Here the expected type is String, which isn't either of those, so the compiler complains about not knowing what the argument type is.
edited Nov 26 '18 at 17:44
Amit Prasad
573315
answered Nov 22 '18 at 11:53
Alexey RomanovAlexey Romanov
108k26213354
add a comment |
You need to use match keyword here to use cases. There might be some value for which you will be using pattern matching. So use the following code in your function:
x match {
case org: String if !ignoredIds.contains(x) => ???
case org : String if ignoredIds.contains(x) => ???
}
Also, you should consider adding one more case which is default. As you know the parameter x of your function def csNotify(x: Any): String is of type any. So anything other than String can also be passed here like Int or Boolean or any custom type. In that case, the code will break with match error.
There will also be a compiler warning saying match is not exhaustive as the current code does not handle all possible values for type Any of parameter x.
But if you add one default case in your pattern matching, all the cases which are not handled by the first two cases (unexpected type or values) will go to the default case. In this way the code will be more robust:
def csNotify(x : Any): String = x match {
case org: String if !ignoredIds.contains(org) => ???
case org : String if ignoredIds.contains(org) => ???
case org => s"unwanted value: $org" // or any default value
}
Note: Kindly replace ??? with your intended code. :)
answered Nov 22 '18 at 11:55
anuj saxenaanuj saxena
24917
add a comment |
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3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
Your case is not finding the match against which it can check your block , and you have missed the match block:
val ignoredIds = Array("one", "two", "three")
def csNotify(x : Any): String = x match {
case org: String if !ignoredIds.contains(x) =>
println( s" $x should not be here")
"one"
case org : String if ignoredIds.contains(x) =>
println(s"$x should be here")
"two"
}
csNotify("four")
So basically when you pass x in method , you have to give it for match as well.
answered Nov 22 '18 at 11:27
Amit PrasadAmit Prasad
573315
add a comment |
Your case is not finding the match against which it can check your block , and you have missed the match block:
val ignoredIds = Array("one", "two", "three")
def csNotify(x : Any): String = x match {
case org: String if !ignoredIds.contains(x) =>
println( s" $x should not be here")
"one"
case org : String if ignoredIds.contains(x) =>
println(s"$x should be here")
"two"
}
csNotify("four")
So basically when you pass x in method , you have to give it for match as well.
answered Nov 22 '18 at 11:27
Amit PrasadAmit Prasad
573315
add a comment |
Your case is not finding the match against which it can check your block , and you have missed the match block:
val ignoredIds = Array("one", "two", "three")
def csNotify(x : Any): String = x match {
case org: String if !ignoredIds.contains(x) =>
println( s" $x should not be here")
"one"
case org : String if ignoredIds.contains(x) =>
println(s"$x should be here")
"two"
}
csNotify("four")
So basically when you pass x in method , you have to give it for match as well.
answered Nov 22 '18 at 11:27
Amit PrasadAmit Prasad
573315
Your case is not finding the match against which it can check your block , and you have missed the match block:
val ignoredIds = Array("one", "two", "three")
def csNotify(x : Any): String = x match {
case org: String if !ignoredIds.contains(x) =>
println( s" $x should not be here")
"one"
case org : String if ignoredIds.contains(x) =>
println(s"$x should be here")
"two"
}
csNotify("four")
So basically when you pass x in method , you have to give it for match as well.
answered Nov 22 '18 at 11:27
Amit PrasadAmit Prasad
573315
answered Nov 22 '18 at 11:27
Amit PrasadAmit Prasad
573315
answered Nov 22 '18 at 11:27
Amit PrasadAmit Prasad
573315
answered Nov 22 '18 at 11:27
Amit PrasadAmit Prasad
573315
573315
add a comment |
add a comment |
Amit Prasad's answer already shows how to fix it, but to explain the error message:
{
case org: String if !ignoredIds.contains(x) =>
println( s" $x should not be here")
"one"
case org : String if ignoredIds.contains(x) =>
println(s"$x should be here")
"two"
}
on its own (without ... match before it) is a pattern-matching anonymous function, which can only be used where the compiler knows the argument type from the context, i.e. the expected type must be either PartialFunction[Something, SomethingElse] or a single-abstract-method type (including Something => SomethingElse).
Here the expected type is String, which isn't either of those, so the compiler complains about not knowing what the argument type is.
edited Nov 26 '18 at 17:44
Amit Prasad
573315
answered Nov 22 '18 at 11:53
Alexey RomanovAlexey Romanov
108k26213354
add a comment |
Amit Prasad's answer already shows how to fix it, but to explain the error message:
{
case org: String if !ignoredIds.contains(x) =>
println( s" $x should not be here")
"one"
case org : String if ignoredIds.contains(x) =>
println(s"$x should be here")
"two"
}
on its own (without ... match before it) is a pattern-matching anonymous function, which can only be used where the compiler knows the argument type from the context, i.e. the expected type must be either PartialFunction[Something, SomethingElse] or a single-abstract-method type (including Something => SomethingElse).
Here the expected type is String, which isn't either of those, so the compiler complains about not knowing what the argument type is.
edited Nov 26 '18 at 17:44
Amit Prasad
573315
answered Nov 22 '18 at 11:53
Alexey RomanovAlexey Romanov
108k26213354
add a comment |
Amit Prasad's answer already shows how to fix it, but to explain the error message:
{
case org: String if !ignoredIds.contains(x) =>
println( s" $x should not be here")
"one"
case org : String if ignoredIds.contains(x) =>
println(s"$x should be here")
"two"
}
on its own (without ... match before it) is a pattern-matching anonymous function, which can only be used where the compiler knows the argument type from the context, i.e. the expected type must be either PartialFunction[Something, SomethingElse] or a single-abstract-method type (including Something => SomethingElse).
Here the expected type is String, which isn't either of those, so the compiler complains about not knowing what the argument type is.
edited Nov 26 '18 at 17:44
Amit Prasad
573315
answered Nov 22 '18 at 11:53
Alexey RomanovAlexey Romanov
108k26213354
Amit Prasad's answer already shows how to fix it, but to explain the error message:
{
case org: String if !ignoredIds.contains(x) =>
println( s" $x should not be here")
"one"
case org : String if ignoredIds.contains(x) =>
println(s"$x should be here")
"two"
}
on its own (without ... match before it) is a pattern-matching anonymous function, which can only be used where the compiler knows the argument type from the context, i.e. the expected type must be either PartialFunction[Something, SomethingElse] or a single-abstract-method type (including Something => SomethingElse).
Here the expected type is String, which isn't either of those, so the compiler complains about not knowing what the argument type is.
edited Nov 26 '18 at 17:44
Amit Prasad
573315
answered Nov 22 '18 at 11:53
Alexey RomanovAlexey Romanov
108k26213354
edited Nov 26 '18 at 17:44
Amit Prasad
573315
edited Nov 26 '18 at 17:44
Amit Prasad
573315
edited Nov 26 '18 at 17:44
Amit Prasad
573315
573315
answered Nov 22 '18 at 11:53
Alexey RomanovAlexey Romanov
108k26213354
answered Nov 22 '18 at 11:53
Alexey RomanovAlexey Romanov
108k26213354
answered Nov 22 '18 at 11:53
Alexey RomanovAlexey Romanov
108k26213354
108k26213354
add a comment |
add a comment |
You need to use match keyword here to use cases. There might be some value for which you will be using pattern matching. So use the following code in your function:
x match {
case org: String if !ignoredIds.contains(x) => ???
case org : String if ignoredIds.contains(x) => ???
}
Also, you should consider adding one more case which is default. As you know the parameter x of your function def csNotify(x: Any): String is of type any. So anything other than String can also be passed here like Int or Boolean or any custom type. In that case, the code will break with match error.
There will also be a compiler warning saying match is not exhaustive as the current code does not handle all possible values for type Any of parameter x.
But if you add one default case in your pattern matching, all the cases which are not handled by the first two cases (unexpected type or values) will go to the default case. In this way the code will be more robust:
def csNotify(x : Any): String = x match {
case org: String if !ignoredIds.contains(org) => ???
case org : String if ignoredIds.contains(org) => ???
case org => s"unwanted value: $org" // or any default value
}
Note: Kindly replace ??? with your intended code. :)
answered Nov 22 '18 at 11:55
anuj saxenaanuj saxena
24917
add a comment |
You need to use match keyword here to use cases. There might be some value for which you will be using pattern matching. So use the following code in your function:
x match {
case org: String if !ignoredIds.contains(x) => ???
case org : String if ignoredIds.contains(x) => ???
}
Also, you should consider adding one more case which is default. As you know the parameter x of your function def csNotify(x: Any): String is of type any. So anything other than String can also be passed here like Int or Boolean or any custom type. In that case, the code will break with match error.
There will also be a compiler warning saying match is not exhaustive as the current code does not handle all possible values for type Any of parameter x.
But if you add one default case in your pattern matching, all the cases which are not handled by the first two cases (unexpected type or values) will go to the default case. In this way the code will be more robust:
def csNotify(x : Any): String = x match {
case org: String if !ignoredIds.contains(org) => ???
case org : String if ignoredIds.contains(org) => ???
case org => s"unwanted value: $org" // or any default value
}
Note: Kindly replace ??? with your intended code. :)
answered Nov 22 '18 at 11:55
anuj saxenaanuj saxena
24917
add a comment |
You need to use match keyword here to use cases. There might be some value for which you will be using pattern matching. So use the following code in your function:
x match {
case org: String if !ignoredIds.contains(x) => ???
case org : String if ignoredIds.contains(x) => ???
}
Also, you should consider adding one more case which is default. As you know the parameter x of your function def csNotify(x: Any): String is of type any. So anything other than String can also be passed here like Int or Boolean or any custom type. In that case, the code will break with match error.
There will also be a compiler warning saying match is not exhaustive as the current code does not handle all possible values for type Any of parameter x.
But if you add one default case in your pattern matching, all the cases which are not handled by the first two cases (unexpected type or values) will go to the default case. In this way the code will be more robust:
def csNotify(x : Any): String = x match {
case org: String if !ignoredIds.contains(org) => ???
case org : String if ignoredIds.contains(org) => ???
case org => s"unwanted value: $org" // or any default value
}
Note: Kindly replace ??? with your intended code. :)
answered Nov 22 '18 at 11:55
anuj saxenaanuj saxena
24917
You need to use match keyword here to use cases. There might be some value for which you will be using pattern matching. So use the following code in your function:
x match {
case org: String if !ignoredIds.contains(x) => ???
case org : String if ignoredIds.contains(x) => ???
}
Also, you should consider adding one more case which is default. As you know the parameter x of your function def csNotify(x: Any): String is of type any. So anything other than String can also be passed here like Int or Boolean or any custom type. In that case, the code will break with match error.
There will also be a compiler warning saying match is not exhaustive as the current code does not handle all possible values for type Any of parameter x.
But if you add one default case in your pattern matching, all the cases which are not handled by the first two cases (unexpected type or values) will go to the default case. In this way the code will be more robust:
def csNotify(x : Any): String = x match {
case org: String if !ignoredIds.contains(org) => ???
case org : String if ignoredIds.contains(org) => ???
case org => s"unwanted value: $org" // or any default value
}
Note: Kindly replace ??? with your intended code. :)
answered Nov 22 '18 at 11:55
anuj saxenaanuj saxena
24917
answered Nov 22 '18 at 11:55
anuj saxenaanuj saxena
24917
answered Nov 22 '18 at 11:55
anuj saxenaanuj saxena
24917
answered Nov 22 '18 at 11:55
anuj saxenaanuj saxena
24917
24917
add a comment |
add a comment |
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