just trying to make a generic uniform cost search ...
# getting-startedh
Hullaballoonatic
09/08/2018, 5:37 PMjust trying to make a generic uniform cost search algorithm
k
karelpeeters
09/08/2018, 5:39 PMUniform cost search? Is that dijksta?
h
Hullaballoonatic
09/08/2018, 5:40 PMuh, it's an AI hw assignment. it's BFS but with an added cost parameter to the states it searches
k
karelpeeters
09/08/2018, 5:42 PMYeah sounds like this one, good luck! https://en.wikipedia.org/wiki/Dijkstra%27s_algorithm?wprov=sfla1
karelpeeters
09/08/2018, 5:45 PMActually you do need addition for that IIRC.
h
Hullaballoonatic
09/08/2018, 5:46 PMyeah, didn't think so
k
karelpeeters
09/08/2018, 5:51 PMIf you really want it to be as generic as possible and aren't worried about performance you'd take a
Comparator<T>add: (T, T) -> T➕ 1
h
Hullaballoonatic
09/08/2018, 5:53 PMI'm getting an error I'm having a hard time putting into words, and I've been fiddling to try and fix it, but coming up empty. can I just show you?
Hullaballoonatic
09/08/2018, 5:54 PMinferred type Pos is not a subtype of IxState<*, Comparable<Any>>Hullaballoonatic
09/08/2018, 5:54 PMPosIxState<Pair<Float, Float>, Float>Hullaballoonatic
09/08/2018, 5:55 PMFloat extends Comparable<Float>
Hullaballoonatic
09/08/2018, 5:55 PMbut I defined the class parameter I'm getting an error on here as
Comparable<*>Hullaballoonatic
09/08/2018, 5:56 PMI'm confused as to what's going on here
k
karelpeeters
09/08/2018, 6:03 PMCould you post a small code example? Just so I'm 100% sure what's going on.
h
Hullaballoonatic
09/08/2018, 6:04 PMin a sec, fiddling more...
Hullaballoonatic
09/08/2018, 6:08 PM Copy code
val searcher = UniformCostSearch(PosComparator(), CostComparator())
class UniformCostSearch<D: Any, C: Comparable<*>>(
dataComp: Comparator<State<D, C>>,
costComp: Comparator<State<D, C>>
)
class PosComparator : Comparator<Pos>
open class Pos: State<Pair<Float, Float>, Float>Hullaballoonatic
09/08/2018, 6:08 PMi left out anything i felt wasn't important
Hullaballoonatic
09/08/2018, 6:09 PMso I get the error when trying to pass
PosComparator()dataCompUniformCostSearchHullaballoonatic
09/08/2018, 6:10 PMright now it says
Copy code
Type mismatch.
Required:
kotlin.Comparator<State<???, ???>> /* = java.util.Comparator<State<???, ???>> */
Found:
PosComparatorHullaballoonatic
09/08/2018, 6:12 PM Copy code
Type inference failed:
constructor UniformCostSearch<D : Any, C : Comparable<*>>
(
dataComp: kotlin.Comparator<State<D, C>> /* = java.util.Comparator<State<D, C>> */,
costComp: kotlin.Comparator<State<D, C>> /* = java.util.Comparator<State<D, C>> */
)
cannot be applied to
(
PosComparator,
CostComparator
)k
karelpeeters
09/08/2018, 6:14 PMOkay so hold, describing what's going wrong with generics is always a ride.
karelpeeters
09/08/2018, 6:15 PMPosComparatorPosPosState<Pair<Float, Float>, Float>karelpeeters
09/08/2018, 6:15 PMBut not every
State<Pair<Float, Float>, Float>Poskarelpeeters
09/08/2018, 6:16 PMUniformCostSearchComparator<State<Pair<Float, Float>, Float>>Comparator<Pos>h
Hullaballoonatic
09/08/2018, 6:18 PMhmmm
Hullaballoonatic
09/08/2018, 6:19 PMdo you have a recommendation? i kinda understand
Hullaballoonatic
09/08/2018, 6:19 PMmaking this generic is not a req for the homework, but I always try to write my programs as generic as possible
k
karelpeeters
09/08/2018, 6:21 PMThe solution here would be to use a type parameter for the state:
Copy code
class UniformCostSearch<S>(
dataComp: Comparator<S>,
costComp: Comparator<S>
)h
Hullaballoonatic
09/08/2018, 6:21 PMAh, thanks
k
karelpeeters
09/08/2018, 6:21 PMAnd if it's really necessary you can put a constraint on S, but is that really the case?
h
Hullaballoonatic
09/08/2018, 6:22 PMI may not need to
Hullaballoonatic
09/08/2018, 6:22 PMi wasn't thinking generic enough i suppose!
k
karelpeeters
09/08/2018, 6:22 PMYeah I have that too sometimes, you end up with all these constrains but none of them are actually useful.
h
Hullaballoonatic
09/08/2018, 6:23 PMthanks a lot!
👍 1
Hullaballoonatic
09/08/2018, 6:29 PMoof, but even if i do that, i can't pass my comparators as constructor arguments... this generic stuff is breaking my brain
k
karelpeeters
09/08/2018, 6:31 PMReally? Works fine for me.
karelpeeters
09/08/2018, 6:31 PM Copy code
interface State<D, C>
val searcher = UniformCostSearch(PosComparator(), PosComparator())
class UniformCostSearch<S>(
dataComp: Comparator<S>,
costComp: Comparator<S>
)
class PosComparator : Comparator<Pos> {
override fun compare(a: Pos, b: Pos) = 0
}
open class Pos: State<Pair<Float, Float>, Float>👍 1
h
Hullaballoonatic
09/08/2018, 6:32 PMI think I know what i have to do
Hullaballoonatic
09/08/2018, 6:33 PMyep
Hullaballoonatic
09/08/2018, 6:33 PMfixed it
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