Custom property delegation for arrays using a map
Consider I'm trying to implement delegation by storing properties in a Map instance, and one of the properties delegated is an array:
class Foo private constructor(map: Map<String, Any?>) {
constructor(value: Array<Byte>) : this(mapOf(Foo::value.name to value))
val value: Array<Byte> by map
}
object PropertyDelegationTest {
@JvmStatic
fun main(vararg args: String) {
val foo = Foo(arrayOf(42.toByte(), 127.toByte()))
println(foo.value[0]) // 42
println(foo.value[1]) // 127
}
}
The above compiles just fine and works as expected.
Now consider I want to enhance my property delegation mechanism by implementing a custom Map.getValue(thisRef: Any?, property: KProperty<*>) extension method (overriding the default extension):
import kotlin.reflect.KProperty
import kotlin.reflect.full.isSubtypeOf
import kotlin.reflect.full.starProjectedType
import kotlin.reflect.jvm.jvmName
// ...
operator fun <V, V1 : V> Map<in String, V>.getValue(thisRef: Any?, property: KProperty<*>): V1 {
val value = this[property.name]
?: throw NoSuchElementException("Key ${property.name} is missing in the map.")
val clazz = (value as Any)::class
@Suppress("UNCHECKED_CAST")
return when {
clazz.starProjectedType.isSubtypeOf(property.returnType) -> value as V1
else -> throw ClassCastException("${clazz.starProjectedType} (${clazz.jvmName}) cannot be cast to ${property.returnType}")
}
}
This fails at run time:
Exception in thread "main" java.lang.ClassCastException: kotlin.Array<*> ([Ljava.lang.Byte;) cannot be cast to kotlin.Array<kotlin.Byte>
at com.example.PropertyDelegationTestKt.getValue(PropertyDelegationTest.kt:30)
at com.example.Foo.getValue(PropertyDelegationTest.kt)
at com.example.PropertyDelegationTest.main(PropertyDelegationTest.kt:18)
Despite the effective JVM type is known ([Ljava.lang.Byte;), Kotlin-specific run time type of the value is Array<*> while Array<Byte> is required. Consistently, clazz.typeParameters[0].upperBounds[0] evaluates to kotlin.Any?, not kotlin.Byte?.
How do I implement my custom type checking which would also work correctly for arrays? Kotlin version is 1.2.71.
arrays kotlin
asked Nov 20 at 9:50
Bass
1,67721646
add a comment |
Consider I'm trying to implement delegation by storing properties in a Map instance, and one of the properties delegated is an array:
class Foo private constructor(map: Map<String, Any?>) {
constructor(value: Array<Byte>) : this(mapOf(Foo::value.name to value))
val value: Array<Byte> by map
}
object PropertyDelegationTest {
@JvmStatic
fun main(vararg args: String) {
val foo = Foo(arrayOf(42.toByte(), 127.toByte()))
println(foo.value[0]) // 42
println(foo.value[1]) // 127
}
}
The above compiles just fine and works as expected.
Now consider I want to enhance my property delegation mechanism by implementing a custom Map.getValue(thisRef: Any?, property: KProperty<*>) extension method (overriding the default extension):
import kotlin.reflect.KProperty
import kotlin.reflect.full.isSubtypeOf
import kotlin.reflect.full.starProjectedType
import kotlin.reflect.jvm.jvmName
// ...
operator fun <V, V1 : V> Map<in String, V>.getValue(thisRef: Any?, property: KProperty<*>): V1 {
val value = this[property.name]
?: throw NoSuchElementException("Key ${property.name} is missing in the map.")
val clazz = (value as Any)::class
@Suppress("UNCHECKED_CAST")
return when {
clazz.starProjectedType.isSubtypeOf(property.returnType) -> value as V1
else -> throw ClassCastException("${clazz.starProjectedType} (${clazz.jvmName}) cannot be cast to ${property.returnType}")
}
}
This fails at run time:
Exception in thread "main" java.lang.ClassCastException: kotlin.Array<*> ([Ljava.lang.Byte;) cannot be cast to kotlin.Array<kotlin.Byte>
at com.example.PropertyDelegationTestKt.getValue(PropertyDelegationTest.kt:30)
at com.example.Foo.getValue(PropertyDelegationTest.kt)
at com.example.PropertyDelegationTest.main(PropertyDelegationTest.kt:18)
Despite the effective JVM type is known ([Ljava.lang.Byte;), Kotlin-specific run time type of the value is Array<*> while Array<Byte> is required. Consistently, clazz.typeParameters[0].upperBounds[0] evaluates to kotlin.Any?, not kotlin.Byte?.
How do I implement my custom type checking which would also work correctly for arrays? Kotlin version is 1.2.71.
arrays kotlin
asked Nov 20 at 9:50
Bass
1,67721646
1
Could you remove the explicit type check and instead do a safe cast toV1and if that fails then throw the exception? e.g.return value as? V1 ?: throw ClassCastException(...?
– Yoni Gibbs
Nov 20 at 11:20
@YoniGibbs This way it works, thanks a lot! Could you convert your comment to an answer so I can up-vote it?
– Bass
Nov 21 at 8:03
add a comment |
Consider I'm trying to implement delegation by storing properties in a Map instance, and one of the properties delegated is an array:
class Foo private constructor(map: Map<String, Any?>) {
constructor(value: Array<Byte>) : this(mapOf(Foo::value.name to value))
val value: Array<Byte> by map
}
object PropertyDelegationTest {
@JvmStatic
fun main(vararg args: String) {
val foo = Foo(arrayOf(42.toByte(), 127.toByte()))
println(foo.value[0]) // 42
println(foo.value[1]) // 127
}
}
The above compiles just fine and works as expected.
Now consider I want to enhance my property delegation mechanism by implementing a custom Map.getValue(thisRef: Any?, property: KProperty<*>) extension method (overriding the default extension):
import kotlin.reflect.KProperty
import kotlin.reflect.full.isSubtypeOf
import kotlin.reflect.full.starProjectedType
import kotlin.reflect.jvm.jvmName
// ...
operator fun <V, V1 : V> Map<in String, V>.getValue(thisRef: Any?, property: KProperty<*>): V1 {
val value = this[property.name]
?: throw NoSuchElementException("Key ${property.name} is missing in the map.")
val clazz = (value as Any)::class
@Suppress("UNCHECKED_CAST")
return when {
clazz.starProjectedType.isSubtypeOf(property.returnType) -> value as V1
else -> throw ClassCastException("${clazz.starProjectedType} (${clazz.jvmName}) cannot be cast to ${property.returnType}")
}
}
This fails at run time:
Exception in thread "main" java.lang.ClassCastException: kotlin.Array<*> ([Ljava.lang.Byte;) cannot be cast to kotlin.Array<kotlin.Byte>
at com.example.PropertyDelegationTestKt.getValue(PropertyDelegationTest.kt:30)
at com.example.Foo.getValue(PropertyDelegationTest.kt)
at com.example.PropertyDelegationTest.main(PropertyDelegationTest.kt:18)
Despite the effective JVM type is known ([Ljava.lang.Byte;), Kotlin-specific run time type of the value is Array<*> while Array<Byte> is required. Consistently, clazz.typeParameters[0].upperBounds[0] evaluates to kotlin.Any?, not kotlin.Byte?.
How do I implement my custom type checking which would also work correctly for arrays? Kotlin version is 1.2.71.
arrays kotlin
asked Nov 20 at 9:50
Bass
1,67721646
Consider I'm trying to implement delegation by storing properties in a Map instance, and one of the properties delegated is an array:
class Foo private constructor(map: Map<String, Any?>) {
constructor(value: Array<Byte>) : this(mapOf(Foo::value.name to value))
val value: Array<Byte> by map
}
object PropertyDelegationTest {
@JvmStatic
fun main(vararg args: String) {
val foo = Foo(arrayOf(42.toByte(), 127.toByte()))
println(foo.value[0]) // 42
println(foo.value[1]) // 127
}
}
The above compiles just fine and works as expected.
Now consider I want to enhance my property delegation mechanism by implementing a custom Map.getValue(thisRef: Any?, property: KProperty<*>) extension method (overriding the default extension):
import kotlin.reflect.KProperty
import kotlin.reflect.full.isSubtypeOf
import kotlin.reflect.full.starProjectedType
import kotlin.reflect.jvm.jvmName
// ...
operator fun <V, V1 : V> Map<in String, V>.getValue(thisRef: Any?, property: KProperty<*>): V1 {
val value = this[property.name]
?: throw NoSuchElementException("Key ${property.name} is missing in the map.")
val clazz = (value as Any)::class
@Suppress("UNCHECKED_CAST")
return when {
clazz.starProjectedType.isSubtypeOf(property.returnType) -> value as V1
else -> throw ClassCastException("${clazz.starProjectedType} (${clazz.jvmName}) cannot be cast to ${property.returnType}")
}
}
This fails at run time:
Exception in thread "main" java.lang.ClassCastException: kotlin.Array<*> ([Ljava.lang.Byte;) cannot be cast to kotlin.Array<kotlin.Byte>
at com.example.PropertyDelegationTestKt.getValue(PropertyDelegationTest.kt:30)
at com.example.Foo.getValue(PropertyDelegationTest.kt)
at com.example.PropertyDelegationTest.main(PropertyDelegationTest.kt:18)
Despite the effective JVM type is known ([Ljava.lang.Byte;), Kotlin-specific run time type of the value is Array<*> while Array<Byte> is required. Consistently, clazz.typeParameters[0].upperBounds[0] evaluates to kotlin.Any?, not kotlin.Byte?.
How do I implement my custom type checking which would also work correctly for arrays? Kotlin version is 1.2.71.
arrays kotlin
arrays kotlin
asked Nov 20 at 9:50
Bass
1,67721646
asked Nov 20 at 9:50
Bass
1,67721646
asked Nov 20 at 9:50
Bass
1,67721646
asked Nov 20 at 9:50
Bass
1,67721646
asked Nov 20 at 9:50
Bass
1,67721646
1,67721646
1
Could you remove the explicit type check and instead do a safe cast toV1and if that fails then throw the exception? e.g.return value as? V1 ?: throw ClassCastException(...?
– Yoni Gibbs
Nov 20 at 11:20
@YoniGibbs This way it works, thanks a lot! Could you convert your comment to an answer so I can up-vote it?
– Bass
Nov 21 at 8:03
add a comment |
1
Could you remove the explicit type check and instead do a safe cast toV1and if that fails then throw the exception? e.g.return value as? V1 ?: throw ClassCastException(...?
– Yoni Gibbs
Nov 20 at 11:20
@YoniGibbs This way it works, thanks a lot! Could you convert your comment to an answer so I can up-vote it?
– Bass
Nov 21 at 8:03
1
1
Could you remove the explicit type check and instead do a safe cast to
V1 and if that fails then throw the exception? e.g. return value as? V1 ?: throw ClassCastException(... ?– Yoni Gibbs
Nov 20 at 11:20
Could you remove the explicit type check and instead do a safe cast to
V1 and if that fails then throw the exception? e.g. return value as? V1 ?: throw ClassCastException(... ?– Yoni Gibbs
Nov 20 at 11:20
@YoniGibbs This way it works, thanks a lot! Could you convert your comment to an answer so I can up-vote it?
– Bass
Nov 21 at 8:03
@YoniGibbs This way it works, thanks a lot! Could you convert your comment to an answer so I can up-vote it?
– Bass
Nov 21 at 8:03
add a comment |
1 Answer
1
active
oldest
votes
You could remove the explicit type check and instead do a safe cast to V1 and if that fails then throw the exception, e.g.
return value as? V1 ?: throw ClassCastException(...
answered Nov 21 at 8:06
Yoni Gibbs
953113
add a comment |
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You could remove the explicit type check and instead do a safe cast to V1 and if that fails then throw the exception, e.g.
return value as? V1 ?: throw ClassCastException(...
answered Nov 21 at 8:06
Yoni Gibbs
953113
add a comment |
You could remove the explicit type check and instead do a safe cast to V1 and if that fails then throw the exception, e.g.
return value as? V1 ?: throw ClassCastException(...
answered Nov 21 at 8:06
Yoni Gibbs
953113
add a comment |
You could remove the explicit type check and instead do a safe cast to V1 and if that fails then throw the exception, e.g.
return value as? V1 ?: throw ClassCastException(...
answered Nov 21 at 8:06
Yoni Gibbs
953113
You could remove the explicit type check and instead do a safe cast to V1 and if that fails then throw the exception, e.g.
return value as? V1 ?: throw ClassCastException(...
answered Nov 21 at 8:06
Yoni Gibbs
953113
answered Nov 21 at 8:06
Yoni Gibbs
953113
answered Nov 21 at 8:06
Yoni Gibbs
953113
answered Nov 21 at 8:06
Yoni Gibbs
953113
953113
add a comment |
add a comment |
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1
Could you remove the explicit type check and instead do a safe cast to
V1and if that fails then throw the exception? e.g.return value as? V1 ?: throw ClassCastException(...?– Yoni Gibbs
Nov 20 at 11:20
@YoniGibbs This way it works, thanks a lot! Could you convert your comment to an answer so I can up-vote it?
– Bass
Nov 21 at 8:03