Kotlin has a `Map MutableMap` which is a `LinkedHashMap` whi kotlinlang #getting-started

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Title

s

Sudhir Singh Khanger

10/15/2019, 5:31 AM

Kotlin has a

Map/MutableMap

which is a

LinkedHashMap

which preserves the insertion order unlike

HashMap

. In Java/Android, if one is used to using

HashMap

then I would think I can continue using

Map/MutableMap

in Kotlin. Is that correct?

d

diesieben07

10/15/2019, 7:03 AM

Yes, both

LinkedHashMap

and

HashMap

implement

MutableMap

, which extends

Map

.

s

Sudhir Singh Khanger

10/15/2019, 8:48 AM

Thanks. In that case, I will use

LinkedHashMap

. Although I don't think I need to maintain order but I might as well use it.

d

diesieben07

10/15/2019, 8:56 AM

If you don't need order, you should use HashMap, it uses less memory than Linked

👍🏽 1

k

karelpeeters

10/15/2019, 8:58 AM

I'm annoyed that

LinkedHashSet

is the default, now everybody is paying this cost all over the code and you need to actively think about using

hashSetOf

instead of

setOf

.

e

eekboom

10/15/2019, 9:25 AM

I assume the performance cost of LinkedHashMap versus HashMap is completely negligible in 99.9% of all cases. IMHO one should not even think about such micro (nano?) optimizations, but rather spend that effort towards cleaner code with better overall organization.

➕ 2

s

Sudhir Singh Khanger

10/16/2019, 4:19 PM

Is there no difference between

linkedMapOf(1 to "z")

and

mapOf(1 to "z")

? Or is

LinkedHashMap

a Java class whereas

Map

is Kotlin class, if there is such a thing, and by extension I should use Kotlin specific classes where ever possible.

k

karelpeeters

10/16/2019, 4:23 PM

linkedMapOf

always returns a

LinkedHashMap

,

mapOf

returns different types for an empty map. Also ´linkedMapOf` is mutable.

But it's a strange situation, sometimes I use

linkedMapOf

to emphasize that the order matters because

mutableMapOf

clearly doesn't signal that.

s

Sudhir Singh Khanger

10/16/2019, 4:41 PM

mapOf
returns different types for an empty map.

What do you mean by different types?

k

karelpeeters

10/16/2019, 4:44 PM

println(mapOf<String, Int>()::class)
println(mapOf<String, Int>("a" to 0)::class)
println(mapOf<String, Int>("a" to 0, "b" to 1)::class)
println(mapOf<String, Int>("a" to 0, "b" to 1, "c" to 2)::class)

//prints:
//kotlin.collections.EmptyMap
//java.util.Collections$SingletonMap
//java.util.LinkedHashMap
//java.util.LinkedHashMap

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