ZH
I am confused with defining custom Functors like RDD
Size: a a a
2020 March 02
λ
Firstly, try to ask your question in the different group -> https://t.me/scala_en
Oℕ
I want to create a custom functor for RDD
It's not possible directly, since RDD requires ClassTag for every operation
Oℕ
I want to create a custom functor for RDD
And Functor requires construction of F[B] from F[A] and A => B without any further information about B.
λ
Олег, ответь в соседний чат ему
ZH
It's not possible directly, since RDD requires ClassTag for every operation
OK any practice example?
Oℕ
OK any practice example?
But you can do:
1. A wrapper for RDD that will accumulate mapping functions and can get back RDD only when you supply a ClassTag
2. Define your own "restricted" or "constrained" version of a functor typeclass. Something like
trait CFunctor[F[_], C[_]]{
def cmap[A, B](fa: F[A])(f : A => B)( implicit ca: C[A], cb: C[B]): F[B]
}
1. A wrapper for RDD that will accumulate mapping functions and can get back RDD only when you supply a ClassTag
2. Define your own "restricted" or "constrained" version of a functor typeclass. Something like
trait CFunctor[F[_], C[_]]{
def cmap[A, B](fa: F[A])(f : A => B)( implicit ca: C[A], cb: C[B]): F[B]
}
Oℕ
OK any practice example?
With further definitions
and
type Dummy[A] = A <:< Any
CFunctor[F, Dummy] will be equivalent to the ordinary Functor[F]and
CFunctor[F, ClassTag] could be implemented for the RDD type constructorZH
so F[_], and C[_] are?
ZH
C[_] is a Custom type for RDD?
Oℕ
Regarding 1. there exists a type for that already:
https://typelevel.org/cats/api/cats/free/Coyoneda.html
Despite fancy name it's just am accumulator of
And can serve as wrapper, providing Functor for any type
https://typelevel.org/cats/api/cats/free/Coyoneda.html
Despite fancy name it's just am accumulator of
map sAnd can serve as wrapper, providing Functor for any type
Oℕ
C[_] is a Custom type for RDD?
C[_] - means "what implicit should I require to map"?
For the most of collections answer is "I don't need any implicit" and you can use the
For RDD answer is "a ClassTag"
For the most of collections answer is "I don't need any implicit" and you can use the
Dummy type above, since implicit value for it is guaranteed and cheapFor RDD answer is "a ClassTag"
Oℕ
so F[_], and C[_] are?
F - is your type constructor, i.e. "List", "Option", "RDD"
ZH
so here take one use case of RDD[String]
ZH
CFunctor[RDD[String], Dummy]
ZH
is it a proper way to use this
Oℕ
So you can define
CFunctor[List, Dummy]
CFunctor[Option, Dummy]
CFunctor[RDD, ClassTag]
CFunctor[TreeSet, Ordering]
CFunctor[List, Dummy]
CFunctor[Option, Dummy]
CFunctor[RDD, ClassTag]
CFunctor[TreeSet, Ordering]
ZH
CFunctor[RDD, String]
ZH
right
ZH
is one use case?