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【Kotlin】KFunctionから定義元objectのinstanceを取得する

Last updated at Posted at 2020-10-24

やりたいこと

KFunctionが渡された時、その定義元がobjectであれば、そのinstanceを取得します。
ただし、今回紹介する方法でトップレベル関数を処理するとjava.lang.UnsupportedOperationExceptionになるため注意が必要です。

やり方

以下のように、KFunctionからjavaMethodを経由することで取得できます。
もう少し素直な取得方法が無いものか確認しましたが、Kotlin 1.4.10時点ではKFunctiondeclaringClassのようなプロパティは無く、無理そうでした。

object Foo {
    fun function(i: Int) = i.toString() 
}

val function: KFunction<String> = (Foo)::function
val instance: Foo = function.javaMethod!!.declaringClass.kotlin.objectInstance as Foo
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