Is there a better more functional way to write this ```peopl

Question

Is there a better more functional way to write this ```people addAll getAllPeople map Pair it first orEmpty it last orEmpty ``` I basically have a variable called people which is a Pair lt gt and then I have the return of getAllPeople which is a Person

Paul Griffith · Answer

`getAllPeople ` only ever returns a 2 element list

Paul Griffith · Answer

~or `getAllPeople ` returns `List lt Pair lt String String gt gt ` and you want `people` to be a `List lt Person gt ` ~ no the opposite of this

Paul Griffith · Answer

the obvious thing to do is to initialize `people` entirely in the `map` call ```val people = getAllPeople map it first to it last ```

Colton Idle · Answer

sorry first and last are firstName and lastName So I m mapping all of the people that come from getAllPeople into Pairs

Paul Griffith · Answer

Paul Griffith · Answer

that s about how I d do it under the assumption it doesn t make sense for your purposes to have someone with an empty first or last name which may or may not be true

Paul Griffith · Answer

see also <https www kalzumeus com 2010 06 17 falsehoods programmers believe about names >

Joffrey · Answer

gt I basically have a variable called people which is a Pair lt gt and then I have the return of getAllPeople which is a Person You mean lists of those things right

Paul Griffith · Answer

on a meta level I m kinda curious why you re after this I find Pair less ergonomic to use and if you ve already got a named class with useful members it s probably easier to hand that around

wbertan · Answer

I would write something like this ```data class People val firstName String val lastName String fun getAllPeople List lt People gt = emptyList fun asas val people = mutableListOf lt Pair lt String String gt gt people addAll getAllPeople map Pair it firstName orEmpty it lastName orEmpty getAllPeople map it firstName orEmpty to it lastName orEmpty let people addAll ``` For me the reason would be to read first what is happening first so basically `getAllPeople` then `map` the `people ddAll` But I would try to avoid the mutable list anyway which would make it nicer to read from the begin Anyway my only suggestion here would be if you could potentially avoid mutability and perhaps can use immutable data there Also what < Paul Griffith> said above

Klitos Kyriacou · Answer

When dealing with Pair firstName lastName I wouldn t use the `to` infix function to create the pair The word to implies a key value relationship First name does not map to surname it s just a pair of names Therefore I would use Pair firstName lastName even though it s slightly longer It s more readable

rook · Answer

`getAllPeople mapTo people `

Colton Idle · Answer

I really like mapTo Thanks that s pretty much what my question was really asking How can I map one list of A to a list of B

Joffrey · Answer

But most of the time you should use read only lists instead of a mutable list So `val mappedList = sourceList map ` is preferable over creating a mutable list first and then using `mapTo`

Joffrey · Answer

I m still quite curious like < Paul Griffith> as to why you want to map those objects to the lesser `Pair` It would seem better to make the properties of `Person` non nullable in the first place or to create an equivalent data class with non nullable fields if you really need the current `Person` class

Paul Griffith · Answer

yeah the more functional way to do things is to not have side effects the transformation of A to B should be the function and `map` should be used to apply it `mapTo` is useful if say you have a collection with some elements already that you can t fit into your starting collection or something like that but in the problem described you don t need and should avoid creating the list and then populating it in two steps

Colton Idle · Answer

Interesting My example I gave isn t what I m actually using in real life it s just as simple of an example as I could come up with But for example some real life examples is that I have a call to getAllMovies and that gives me back a list of MovieDTO Now I want to map my MovieDTOs into MovieUI objects So I m just looking for how to map between two very similar classes but are different classes

Joffrey · Answer

Ok that answers the `Pair` stuff then The `mapTo` vs `map` still holds though In the case you mention you should use `map`

Colton Idle · Answer

Okay So if my map just transforms from ObjectA to ObjectB then the output will just be a List lt ObjectB gt and then I can addAll to my variable of listOfObjectB

Joffrey · Answer

Sorry if I was unclear If your goal really is to add to a mutable list then of course `mapTo` is what should be used instead to avoid an extra list But our point was that if you don t already have a mutable list you should probably not create a mutable list at all and just use the result of map directly