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#getting-started
Title
# getting-started
c

Colton Idle

04/11/2022, 10:51 PM
If I have
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val data =
    hashMapOf(
            "firstName" to firstName,
            "lastName" to lastName)
but I wanted to not add firstName or lastName to the hashmap if they are null. What would be the best way to do that?
e

ephemient

04/11/2022, 10:58 PM
must it be a HashMap or are other maps allowed?
j

Joffrey

04/11/2022, 10:58 PM
Do you really need an explicit
java.util.HashMap
as output? In general it's more common to stick with
mapOf
or
mutableMapOf
. When building a read-only map, you can use
buildMap
with conditions inside:
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val map = buildMap {
    firstName?.let { put("firstName", it) }
    lastName?.let { put("lastName", it) }
}
If what you need is a mutable map, you can also add stuff conditionally with `apply`:
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val map = mutableMapOf<String, String>().apply {
    firstName?.let { put("firstName", it) }
    lastName?.let { put("lastName", it) }
}
c

Colton Idle

04/11/2022, 11:00 PM
I'm following firebases docs which have a hashMapOf, but I suppose I can try other maps? Shouldn't be an issue.
e

ephemient

04/11/2022, 11:01 PM
also options,
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buildMap {
    firstName?.let { put("firstName", it) }
    lastName?.let { put("lastName", it) }
}

@Suppress("UNCHECKED_CAST")
fun <K, V> Map<K, V?>.filterNotNullValues(): Map<K, V> = filterValues { it != null } as Map<K, V>

mapOf("firstName" to firstName, "lastName" to lastName).filterNotNullValues()
https://firebase.google.com/docs/reference/android/com/google/firebase/functions/HttpsCallableReference#call(java.lang.Object)
The data passed into the trigger can be any of the following types:
• Any primitive type, including null, int, long, float, and boolean.
String
List<?>
, where the contained objects are also one of these types.
Map<String, ?>>
, where the values are also one of these types.
JSONArray
JSONObject
NULL
you do not need a HashMap, that Kotlin example was simply translated from Java
c

Colton Idle

04/11/2022, 11:03 PM
Thanks. I like the conciseness of just having the ext func. But TIL about buildMap!
r

Ruckus

04/11/2022, 11:04 PM
You can always make a helper function:
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fun <K: Any, V: Any> nonNullHashMapOf(
    vararg entries: Pair<K?, V?>
): HashMap<K, V> {
    val map = HashMap<K, V>()
    for ((key, value) in entries) {
        map[key ?: continue] = value ?: continue
    }
    return map
}
And use it
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val data = nonNullHashMapOf(
    "firstName" to firstName,
    "lastName" to lastName,
)
e

ephemient

04/11/2022, 11:05 PM
I would name it as
mapOfNotNull
just to match
listOfNotNull
better, but yeah that can also be done
c

Colton Idle

04/11/2022, 11:05 PM
Oooh boy! So many options!
e
r

Ruckus

04/11/2022, 11:06 PM
@ephemient That's probably a good idea. I'm not great at naming (like most programmers...)
e

ephemient

04/11/2022, 11:06 PM
I'm not great either, I'm just copying stdlib here :)
😁 1
c

Colton Idle

04/11/2022, 11:09 PM
If I use
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fun <K: Any, V: Any> nonNullHashMapOf(vararg entries: Pair<K?, V?>) {
    val map = HashMap<K, V>()
    for ((key, value) in entries) {
        map[key ?: continue] = value ?: continue
    }
}
should I try to use a Regular map internally, or is HashMap alright?
r

Ruckus

04/11/2022, 11:10 PM
Use a hash map if you need a hash map for some reason, otherwise just use
mutableMapOf<K, V>()
e

ephemient

04/11/2022, 11:10 PM
if your function is named
hashMapOf
it should probably return a
HashMap
to reduce confusion 😛
r

Ruckus

04/11/2022, 11:11 PM
(By the way, I update my comment to include the return value, which I forgot the first time.)
e

ephemient

04/11/2022, 11:11 PM
in practice
MutableMap
is backed by a
LinkedHashMap
, so it is a
HashMap
in a sense
(but that's not a public API contract so don't rely on it)
2
c

Colton Idle

04/11/2022, 11:13 PM
Okay, so I'm using @Ruckus method you outlined, but @ephemient naming (stdlib naming). Anything else I should do to improve? (the only reason I asked about converting this to a regular Map instead of HashMap was because that was in the opening comment.
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fun <K: Any, V: Any> mapOfNotNull(
    vararg entries: Pair<K?, V?>
): HashMap<K, V> {
    val map = HashMap<K, V>()
    for ((key, value) in entries) {
        map[key ?: continue] = value ?: continue
    }
    return map
}
r

Ruckus

04/11/2022, 11:13 PM
If you don't need a hash map:
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fun <K: Any, V: Any> mapOfNotNull(
    vararg entries: Pair<K?, V?>
): Map<K, V> = buildMap {
    for ((key, value) in entries) {
        this[key ?: continue] = value ?: continue
    }
}
c

Colton Idle

04/11/2022, 11:15 PM
@ephemient I'll file a bug fore firebase docs to just be mapOf instead of hashMapOf
r

Ruckus

04/11/2022, 11:17 PM
With the new definitely non null types, this could also be
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fun <K, V> mapOfNotNull(
    vararg entries: Pair<K, V>
): Map<K & Any, V & Any> = buildMap {
    for ((key, value) in entries) {
        this[key ?: continue] = value ?: continue
    }
}
Though I don't know if that's any better... https://blog.jetbrains.com/kotlin/2022/04/kotlin-1-6-20-released/#definitely-non-nullable-types
c

Colton Idle

04/11/2022, 11:19 PM
TIL "Definitely non-nullable types"
I'm going to go with this for now. Learned a ton in the past 15 minutes. Filed a bug. Thanks everyone for teaching!
👍 1
l

Landry Norris

04/12/2022, 9:39 PM
Just in case it’s helpful, GitLive has a library that lets you read and write kotlinx.serialization objects to/from firebase instead of using the HashMap based API. https://firebaseopensource.com/projects/gitliveapp/firebase-kotlin-sdk/
👍 1
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