kotlinでif文の条件に代入式を使いたい ref: https://qiita.com/itmammoth/items/e21dba17373e0aa7353e

file0.txt

if (val date = arguments?.getSerializable(ARG_DATE) as LocalDate) {
    ...

file1.txt

inline fun <T, R> ifNotNull(value: T?, thenPart: (T) -> R, elsePart: () -> R): R {
    return if (value != null) {
        thenPart(value)
    } else {
        elsePart()
    }
}

file2.txt

val thenOrElse = ifNotNull(arguments?.getSerializable(ARG_DATE) as? LocalDate, {
    // it => LocalDate
    "then"
}, {
    "else"
})

file3.txt

inline fun <T, R> ifNotNull(value: T?, thenPart: (T) -> R): R? {
    return if (value != null) {
        thenPart(value)
    } else {
        null
    }
}

ifNotNull

inline fun <T, R> ifNotNull(value: T?, thenPart: (T) -> R, elsePart: () -> R): R {
    return if (value != null) {
        thenPart(value)
    } else {
        elsePart()
    }
}

You can write as below with this function.

val thenOrElse = ifNotNull(arguments?.getSerializable("date") as? LocalDate, {
    // it => LocalDate
    "then"
}, {
    "else"
})