I swear I have long covid and brain fog or something Is ther

Question

I swear I have long covid and brain fog or something Is there an idiomatic way in Kotlin to `map` while supplying the map like operation with a list of functions or vararg to apply to each element rather than a single transformation basically ~`collection mapAll transformers List lt T gt R gt `~ `sequence mapAll transformers List lt T gt T gt ` I want to supply a list of transformers so I don t have to do something like ```sequence map first map second map third ``` would be ```sequence map tranformers ```

Joffrey · Answer

I don t think there is any built in stdlib function to do that directly But you could implement your own Note that `List lt T gt R gt ` cannot work in general though because you would need each function s output type to be the same or a subtype of the next function s input type

wbertan · Answer

thinking face if you are mapping you are changing the types so I don t see this list of transformers working how would the compiler ensure the types

wbertan · Answer

Would `Sequence` not handle this case without having to make multiple iterations thinking face

denis · Answer

If I m not mistaken there is a common rule if you have more than 2 transform operators you d better use a sequence

Alan B · Answer

I may be approaching the problem incorrectly The input type in each transformer is the the same as the output It s basically like a reducer but I keep each element Each function has a responsibility to calculate some specific business rule and applies its value to an accumulator

Alan B · Answer

I am using a sequence

Alan B · Answer

I should change the collection to sequence in my example

denis · Answer

extension functions to the rescue

Alan B · Answer

Ok I thought there might be a way to just simply apply a list of functions with an argument like a chain where the output is the input of the next in the list

Joffrey · Answer

If the types are all the same one way to roll your own is the following ```fun lt T gt Sequence lt T gt map transforms List lt T gt T gt Sequence lt T gt = transforms fold this s t gt s map t ``` See <https pl kotl in clSuDg4m0>

Alan B · Answer

hah thanks

Joffrey · Answer

Note that this `fold` is not operating on the sequence but on the list of transformations so it builds a new sequence by repeatedly applying `map` with each transform The initial value for the fold is the initial sequence

Alan B · Answer

hmmm I ll have to think about that one

Alan B · Answer

Thanks all for info At least I know there isn t a native way to apply this Again I am pretty sure I might be doing something wrong but I am just working on a PoC for extracting and reporting on data from an external system in a concise and extensible way to supply new functionality without modifying the execution code

Alan B · Answer

And I wasn t kidding about the brain fog It s like I used to be able to play chess think a few moves ahead and now I can only imagine one or two It s odd Hah All the caffeine in the world doesn t help

Alan B · Answer

BTW I also fixed the signature as it was wrong It should have always been ` T gt T` not ` T gt R` for my example

Klitos Kyriacou · Answer

Another way ```sequence map it let transform1 let transform2 let transform3 ``` This also works just as well with collections as it transforms it element by element

Alan B · Answer

I need to pass a collection of functions The list is unknown until it s executed

ephemient · Answer

you could fold over the transforms while mapping each individual element ```fun lt T gt Sequence lt T gt map transforms Iterable lt T gt T gt Sequence lt T gt = map transforms fold it s t gt s map t ```