How scala HashMap inherit the “++” method while both superclasses TraversableLike and MapLike has same...
When I was learning Scala source code of version 2.11.8, I found aspect of HashMap which confused me:
I noticed that there are 2 traits of HashMap for mixin directly or indirectly, which both defined ++ method:
TraversableLikeMapLike
It seems that these 2 traits both take GenTraversableOnce type as parameter, but with difference that TraversableLike trait defined one more parameter list for implicit CanBuildFrom, however in HashMap.scala, there is also defined an implicit CanBuildFrom in scope, but I have NO idea which ++ method HashMap will inherit from between these 2 traits, i.e. whether to use implicit CanBuildFrom or not. Please, see bellow my test example:
//the paramter list for implicit ev is just evidence to limit the (A,B) as subtypes of (Int,String), to confirm with the expected return type.
def addElements1[A,B](t: (A,B)*)(implicit ev: <:<[(A,B),(Int,String)]): HashMap[Int,String] = {
val h = new HashMap[Int,String]
h ++ t
h
}
def addElements2[A,B](t: (A,B)*): HashMap[A,B] = {
val h = new HashMap[A,B]
h ++ t
h
}
def main(args: Array[String]): Unit = {
addElements1((1,"a"),(2,"b"),(3,"c"))
addElements2((4,"d"),(5,"e"),(6,"f"))
}
During debug process, I got different results of there 2 method, that is, the method addElements1 inherits the method ++ from trait TraversableLike. Method addElements2 inherits the method ++ from trait MapLike.
Is there obvious rule or condition for which method should me used for HashMap?
FYI: The inheritance chain of HashMap from these 2 traits are:
HashMap <- MapLike
HashMap <- Map <- Iterable <- Traversable <- TraversableLike
Thanks a lot for all your effort on this question in advance.
scala hashmap scala-collections
edited Nov 23 at 11:07
ygor
911514
asked Nov 23 at 10:06
Jason L
111
add a comment |
When I was learning Scala source code of version 2.11.8, I found aspect of HashMap which confused me:
I noticed that there are 2 traits of HashMap for mixin directly or indirectly, which both defined ++ method:
TraversableLikeMapLike
It seems that these 2 traits both take GenTraversableOnce type as parameter, but with difference that TraversableLike trait defined one more parameter list for implicit CanBuildFrom, however in HashMap.scala, there is also defined an implicit CanBuildFrom in scope, but I have NO idea which ++ method HashMap will inherit from between these 2 traits, i.e. whether to use implicit CanBuildFrom or not. Please, see bellow my test example:
//the paramter list for implicit ev is just evidence to limit the (A,B) as subtypes of (Int,String), to confirm with the expected return type.
def addElements1[A,B](t: (A,B)*)(implicit ev: <:<[(A,B),(Int,String)]): HashMap[Int,String] = {
val h = new HashMap[Int,String]
h ++ t
h
}
def addElements2[A,B](t: (A,B)*): HashMap[A,B] = {
val h = new HashMap[A,B]
h ++ t
h
}
def main(args: Array[String]): Unit = {
addElements1((1,"a"),(2,"b"),(3,"c"))
addElements2((4,"d"),(5,"e"),(6,"f"))
}
During debug process, I got different results of there 2 method, that is, the method addElements1 inherits the method ++ from trait TraversableLike. Method addElements2 inherits the method ++ from trait MapLike.
Is there obvious rule or condition for which method should me used for HashMap?
FYI: The inheritance chain of HashMap from these 2 traits are:
HashMap <- MapLike
HashMap <- Map <- Iterable <- Traversable <- TraversableLike
Thanks a lot for all your effort on this question in advance.
scala hashmap scala-collections
edited Nov 23 at 11:07
ygor
911514
asked Nov 23 at 10:06
Jason L
111
add a comment |
When I was learning Scala source code of version 2.11.8, I found aspect of HashMap which confused me:
I noticed that there are 2 traits of HashMap for mixin directly or indirectly, which both defined ++ method:
TraversableLikeMapLike
It seems that these 2 traits both take GenTraversableOnce type as parameter, but with difference that TraversableLike trait defined one more parameter list for implicit CanBuildFrom, however in HashMap.scala, there is also defined an implicit CanBuildFrom in scope, but I have NO idea which ++ method HashMap will inherit from between these 2 traits, i.e. whether to use implicit CanBuildFrom or not. Please, see bellow my test example:
//the paramter list for implicit ev is just evidence to limit the (A,B) as subtypes of (Int,String), to confirm with the expected return type.
def addElements1[A,B](t: (A,B)*)(implicit ev: <:<[(A,B),(Int,String)]): HashMap[Int,String] = {
val h = new HashMap[Int,String]
h ++ t
h
}
def addElements2[A,B](t: (A,B)*): HashMap[A,B] = {
val h = new HashMap[A,B]
h ++ t
h
}
def main(args: Array[String]): Unit = {
addElements1((1,"a"),(2,"b"),(3,"c"))
addElements2((4,"d"),(5,"e"),(6,"f"))
}
During debug process, I got different results of there 2 method, that is, the method addElements1 inherits the method ++ from trait TraversableLike. Method addElements2 inherits the method ++ from trait MapLike.
Is there obvious rule or condition for which method should me used for HashMap?
FYI: The inheritance chain of HashMap from these 2 traits are:
HashMap <- MapLike
HashMap <- Map <- Iterable <- Traversable <- TraversableLike
Thanks a lot for all your effort on this question in advance.
scala hashmap scala-collections
edited Nov 23 at 11:07
ygor
911514
asked Nov 23 at 10:06
Jason L
111
When I was learning Scala source code of version 2.11.8, I found aspect of HashMap which confused me:
I noticed that there are 2 traits of HashMap for mixin directly or indirectly, which both defined ++ method:
TraversableLikeMapLike
It seems that these 2 traits both take GenTraversableOnce type as parameter, but with difference that TraversableLike trait defined one more parameter list for implicit CanBuildFrom, however in HashMap.scala, there is also defined an implicit CanBuildFrom in scope, but I have NO idea which ++ method HashMap will inherit from between these 2 traits, i.e. whether to use implicit CanBuildFrom or not. Please, see bellow my test example:
//the paramter list for implicit ev is just evidence to limit the (A,B) as subtypes of (Int,String), to confirm with the expected return type.
def addElements1[A,B](t: (A,B)*)(implicit ev: <:<[(A,B),(Int,String)]): HashMap[Int,String] = {
val h = new HashMap[Int,String]
h ++ t
h
}
def addElements2[A,B](t: (A,B)*): HashMap[A,B] = {
val h = new HashMap[A,B]
h ++ t
h
}
def main(args: Array[String]): Unit = {
addElements1((1,"a"),(2,"b"),(3,"c"))
addElements2((4,"d"),(5,"e"),(6,"f"))
}
During debug process, I got different results of there 2 method, that is, the method addElements1 inherits the method ++ from trait TraversableLike. Method addElements2 inherits the method ++ from trait MapLike.
Is there obvious rule or condition for which method should me used for HashMap?
FYI: The inheritance chain of HashMap from these 2 traits are:
HashMap <- MapLike
HashMap <- Map <- Iterable <- Traversable <- TraversableLike
Thanks a lot for all your effort on this question in advance.
scala hashmap scala-collections
scala hashmap scala-collections
edited Nov 23 at 11:07
ygor
911514
asked Nov 23 at 10:06
Jason L
111
edited Nov 23 at 11:07
ygor
911514
asked Nov 23 at 10:06
Jason L
111
edited Nov 23 at 11:07
ygor
911514
edited Nov 23 at 11:07
ygor
911514
edited Nov 23 at 11:07
ygor
911514
911514
asked Nov 23 at 10:06
Jason L
111
asked Nov 23 at 10:06
Jason L
111
asked Nov 23 at 10:06
Jason L
111
111
add a comment |
add a comment |
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