Questions tagged [path-dependent-type]
152 questions
4
votes
3 answers
Is a Path Dependent Type a subtype?
trait A {
trait B {
def foo: A.this.B = new B{}
def bar: A#B = foo
def baz: A.this.B = bar // type mismatch; found : A#B required: A.this.B
}
}
Am I right that A.this.B is a path dependent type?! (That's my understanding so…
Peter Schmitz
- 5,734
- 4
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4
votes
3 answers
Driving a singleton type through a brickwall
Here is a very condensed version:
case class Brickwall[A](otherSide: A)
trait Monoman { def me(m: this.type): Unit }
def test(m: Monoman): Unit = m.me(Brickwall(m).otherSide)
-> error: type mismatch;
found : Monoman
required: m.type
stupid…
0__
- 64,257
- 16
- 158
- 253
4
votes
2 answers
Scala Dependent type does not compile
This code should compile in Scala:
trait Pipe {
type Input
type Output
def apply(input: Input): Output
}
object Pipe {
trait Start extends Pipe {
override type Input = Seq[String]
}
abstract class Connect(val prev: Pipe) extends…
pathikrit
- 29,060
- 33
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4
votes
1 answer
How to use path-dependent types with type classes in Scala
I’m having some problems with path dependent types.
I have some types Foo with an abstract type member F. Instances such as Bar will provide the concrete type.
Then there is a type class Baz. I have instances of the type class for each concrete type…
steinybot
- 3,745
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- 43
4
votes
1 answer
Objects with type members: what is Scala's object vs module system ? (Trying to understand a 2014 Odersky paper on path dependent types)
I am reading Foundations of path dependent types. On the first page, on the right column it is written:
Our motivation is twofold. First, we believe objects with type members
are not fully understood. It is not clear what causes the complexity,
…
jhegedus
- 18,516
- 11
- 84
- 147
4
votes
1 answer
In Scala, how can I restrict multiple parameters must be a type inside the same type?
I'm trying to use path dependent type with generics.
I have two classes, the class C2 is nested in C1.
case class C1(v1: Int) {
case class C2(v2: Int)
}
And I have two object of class C1 here:
object O1 extends C1(1)
object O2 extends C1(2)
I…
lxohi
- 320
- 2
- 11
4
votes
2 answers
Scala: implicit lookup of type class instance for path-dependent type
trait Encoder[From, To] {
def encode(x: From): To
}
object Encoder {
implicit val thingToString: Encoder[Thing, String] = new Encoder[Thing, String] {
def encode(x: Thing): String = x.toString
}
}
trait Config {
type Repr
}
class…
Chris B
- 8,939
- 4
- 30
- 36
4
votes
2 answers
Path-dependent typing over match/case
sealed trait Desc {
type T
}
trait Dataset[A] {
def toDS[A] = new Dataset[A] {}
}
trait DataFrame {}
sealed trait DFDesc extends Desc {
type T = Dummy
}
sealed trait DSDesc[A] extends Desc {
type T = A
}
trait JobConstruction {
def…
Reactormonk
- 20,410
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- 110
4
votes
1 answer
Composing type-level functions with implicit witnesses
I am experimenting with some rather complex type-level calculations. There, I have some type tags (say, A, B, and C), and functions working on them, which are represented by implicit witnesses with path-dependent result types:
class A
class B
class…
phipsgabler
- 16,452
- 4
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- 52
4
votes
1 answer
Type mismatch with type projection
I'm having a compiler type mismatch error that I do not understand.
Given the following definition of an Elem and a factory (Companion):
object Elem {
trait Companion[E[~] <: Elem[~]] {
def apply[S](peer: E[S]#Peer): E[S] // wrap a peer in its…
0__
- 64,257
- 16
- 158
- 253
4
votes
1 answer
Unable to resolve path dependent type class evidence w/o having value type accessible
I got stuck for like an hour to discover this fact:
class Foo {
trait TypeClass[X]
object TypeClass {
implicit val gimme = new TypeClass[Int]{}
}
def foo[X : TypeClass](p: X): Unit = println("yeah " + p)
}
// compiles
val foo =…
lisak
- 20,109
- 39
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- 236
4
votes
1 answer
Deep conversion of Map to TreeMap
I need to convert arbitrary nested Map to TreeMap. Examples:
Map[Int, String] -> TreeMap[Int, String]
Map[Int, Map[Int, String]] -> TreeMap[Int, TreeMap[Int, String]]
... etc
I've got working solution with type gymnastics and implicit conversions,…
Eugene Zhulenev
- 9,469
- 2
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- 38
4
votes
2 answers
Why scala compiler doesn't infer type with abstract type
Given the following code
trait A { type B }
case class C extends A { type B = String }
def f[V <: A](b: V#B => V) = b
This one compile
f[C](a => new C())
But why this one doesn't compile ?
f(a => new C())
Yann Moisan
- 7,685
- 6
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- 83
4
votes
1 answer
Implicit conversions for members that are types
given:
implicit class WithRetType[T, U](x: T => U) {
type Ret = U
}
this:
val foo = (_: Int) * 2
val x: foo.Ret = 3
yields:
error: type Ret is not a member of Int => Int
val x: foo.Ret = ???
^
the following however works:
val foo =…
Erik Kaplun
- 33,421
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- 102
4
votes
1 answer
Chaining path-dependent types and instantiating them when they having different parameter lists in Scala
I'm experimenting with writing more statically type-safe code by implementing a simple card game. In this game, there are several unique cards and each card has a card-specific effect which may require additional parameters (e.g., a target for the…
Jonathan Chow
- 105
- 3