return false in anonymous lambda

Question

This is my code.

fun isJoined(user: User): Boolean {
    val member = requireNotNull(guild.getMember(user)) { return false }
    return joined.contains(member)
}

When member is null, is the funtion 'isJoined' returns false or just anonymous function returns false (so that member to be false)?
If anonymous function returns false, then how can I change my code to return the function 'isJoined'?

score 2 · Accepted Answer · answered Nov 14 '20 at 13:28

2

In Kotlin, lambdas with a return automatically default to returning from the innermost function, which means that your entire function will return false. Read here for more info. Also, the elvis operator provides a more elegant way to write this:

val member = guild.getMember(user) ?: return false

answered Nov 14 '20 at 13:28

Aplet123

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Thank you for your answer. Have a nice day :D – nkgcp Nov 15 '20 at 00:36

score 0 · Answer 2 · answered Nov 14 '20 at 13:48

You can re-write your isJoined() function like this:

fun isJoined(user: User): Boolean =
    guild.getMember(user)?.let { joined.contains(it) } == true

It will do the following things:

When guid.GetMember() returns a member, it calls joined.contains(member), which will return a boolean. Comparing a boolean with == true is a noop, so the result of contains(member) is returned.
When guild.GetMember() returns null, the let block is not called, and the expression becomes null == true, which returns false.

It's equivalent to this:

fun isJoined(user: User): Boolean {
    val nullableMember = guild.getMember(user)
    return if (nullableMember == null) false else joined.contains(nullableMember)
}

return false in anonymous lambda

2 Answers2