KT.MULTILINE_LAMBDA_IT_PARAMETER

Multi-line lambda with explicit usages of the 'it' parameter

Lambda expressions are very useful in a lot of cases, and they often include very small chunks of code using only one parameter. In this cases Kotlin can supply the implicit 'it' parameter to make code more concise. However, when you are dealing with lambdas that contain multiple statements, you might end up with code that is hard to read if you don't specify a readable, descriptive parameter name explicitly.

Noncompliant Code

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val digits = 1234.let {
    println(it)
    listOf(it)
}

val digits = 1234.let { it ->
    println(it)
    listOf(it)
}

val flat = listOf(listOf(1), listOf(2)).mapIndexed { index, it ->
    println(it)
    it + index
}

Compliant Code

Copy

val digits = 1234.let { explicitParameterName ->
    println(explicitParameterName)
    listOf(explicitParameterName)
}

val lambda = { item: Int, that: String ->
    println(item)
    item.toString() + that
}

val digits = 1234.let { listOf(it) }
val digits = 1234.let {
    listOf(it)
}
val digits = 1234.let { it -> listOf(it) }
val digits = 1234.let { it ->
    listOf(it)
}
val digits = 1234.let { explicit -> listOf(explicit) }
val digits = 1234.let { explicit ->
    listOf(explicit)
}