just trying to make a generic uniform cost search algorithm

Question

karelpeeters · Answer

Uniform cost search Is that dijksta

Hullaballoonatic · Answer

uh it s an AI hw assignment it s BFS but with an added cost parameter to the states it searches

karelpeeters · Answer

Yeah sounds like this one good luck <https en wikipedia org wiki Dijkstra 27s algorithm wprov=sfla1>

karelpeeters · Answer

Actually you do need addition for that IIRC

Hullaballoonatic · Answer

yeah didn t think so

karelpeeters · Answer

If you really want it to be as generic as possible and aren t worried about performance you d take a `Comparator lt T gt ` and an `add T T gt T`

Hullaballoonatic · Answer

I 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 · Answer

`inferred type Pos is not a subtype of IxState lt Comparable lt Any gt gt `

Hullaballoonatic · Answer

`Pos` extends this `IxState lt Pair lt Float Float gt Float gt `

Hullaballoonatic · Answer

Float extends Comparable lt Float gt

Hullaballoonatic · Answer

but I defined the class parameter I m getting an error on here as `Comparable lt gt `

Hullaballoonatic · Answer

I m confused as to what s going on here

karelpeeters · Answer

Could you post a small code example Just so I m 100 sure what s going on

Hullaballoonatic · Answer

in a sec fiddling more

Hullaballoonatic · Answer

``` val searcher = UniformCostSearch PosComparator CostComparator class UniformCostSearch lt D Any C Comparable lt gt gt dataComp Comparator lt State lt D C gt gt costComp Comparator lt State lt D C gt gt class PosComparator Comparator lt Pos gt open class Pos State lt Pair lt Float Float gt Float gt ```

Hullaballoonatic · Answer

i left out anything i felt wasn t important

Hullaballoonatic · Answer

so I get the error when trying to pass `PosComparator ` as `dataComp` in `UniformCostSearch`

Hullaballoonatic · Answer

right now it says ```Type mismatch Required kotlin Comparator lt State lt gt gt = java util Comparator lt State lt gt gt Found PosComparator```

Hullaballoonatic · Answer

```Type inference failed constructor UniformCostSearch lt D Any C Comparable lt gt gt dataComp kotlin Comparator lt State lt D C gt gt = java util Comparator lt State lt D C gt gt costComp kotlin Comparator lt State lt D C gt gt = java util Comparator lt State lt D C gt gt cannot be applied to PosComparator CostComparator ```

karelpeeters · Answer

Okay so hold describing what s going wrong with generics is always a ride

karelpeeters · Answer

`PosComparator` can compare `Pos` instances and `Pos` instances are also `State lt Pair lt Float Float gt Float gt ` instances

karelpeeters · Answer

But not every `State lt Pair lt Float Float gt Float gt ` is also a `Pos`

karelpeeters · Answer

`UniformCostSearch` would need a `Comparator lt State lt Pair lt Float Float gt Float gt gt ` here but you only provide a `Comparator lt Pos gt `

Hullaballoonatic · Answer

hmmm

Hullaballoonatic · Answer

do you have a recommendation i kinda understand

Hullaballoonatic · Answer

making this generic is not a req for the homework but I always try to write my programs as generic as possible

karelpeeters · Answer

The solution here would be to use a type parameter for the state ```class UniformCostSearch lt S gt dataComp Comparator lt S gt costComp Comparator lt S gt ```

Hullaballoonatic · Answer

Ah thanks

karelpeeters · Answer

And if it s really necessary you can put a constraint on S but is that really the case

Hullaballoonatic · Answer

I may not need to

Hullaballoonatic · Answer

i wasn t thinking generic enough i suppose

karelpeeters · Answer

Yeah I have that too sometimes you end up with all these constrains but none of them are actually useful

Hullaballoonatic · Answer

thanks a lot

Hullaballoonatic · Answer

oof but even if i do that i can t pass my comparators as constructor arguments this generic stuff is breaking my brain

karelpeeters · Answer

Really Works fine for me

karelpeeters · Answer

```interface State lt D C gt val searcher = UniformCostSearch PosComparator PosComparator class UniformCostSearch lt S gt dataComp Comparator lt S gt costComp Comparator lt S gt class PosComparator Comparator lt Pos gt override fun compare a Pos b Pos = 0 open class Pos State lt Pair lt Float Float gt Float gt ```

Hullaballoonatic · Answer

I think I know what i have to do

Hullaballoonatic · Answer

yep

Hullaballoonatic · Answer

fixed it