Reflection: add KClass.isInstance, KClass.cast, KClass.safeCast

#KT-11284 Fixed

core/reflection.jvm/src/kotlin/reflect/KClasses.kt

@@ -236,3 +236,29 @@ fun KClass<*>.isSubclassOf(base: KClass<*>): Boolean =
  */
 fun KClass<*>.isSuperclassOf(derived: KClass<*>): Boolean =
         derived.isSubclassOf(this)
+
+
+/**
+ * Casts the given [value] to the class represented by this [KClass] object.
+ * Throws an exception if the value is `null` or if it is not an instance of this class.
+ *
+ * @see [KClass.isInstance]
+ * @see [KClass.safeCast]
+ */
+@Suppress("UNCHECKED_CAST")
+fun <T : Any> KClass<T>.cast(value: Any?): T {
+    if (!isInstance(value)) throw TypeCastException("Value cannot be cast to $qualifiedName")
+    return value as T
+}
+
+/**
+ * Casts the given [value] to the class represented by this [KClass] object.
+ * Returns `null` if the value is `null` or if it is not an instance of this class.
+ *
+ * @see [KClass.isInstance]
+ * @see [KClass.cast]
+ */
+@Suppress("UNCHECKED_CAST")
+fun <T : Any> KClass<T>.safeCast(value: Any?): T? {
+    return if (isInstance(value)) value as T else null
+}

core/reflection.jvm/src/kotlin/reflect/jvm/internal/KClassImpl.kt

@@ -20,6 +20,8 @@ import org.jetbrains.kotlin.descriptors.*
 import org.jetbrains.kotlin.descriptors.annotations.Annotated
 import org.jetbrains.kotlin.incremental.components.NoLookupLocation
 import org.jetbrains.kotlin.load.java.JvmAbi
+import org.jetbrains.kotlin.load.java.structure.reflect.functionClassArity
+import org.jetbrains.kotlin.load.java.structure.reflect.wrapperByPrimitive
 import org.jetbrains.kotlin.load.kotlin.header.KotlinClassHeader
 import org.jetbrains.kotlin.load.kotlin.reflect.ReflectKotlinClass
 import org.jetbrains.kotlin.name.ClassId
@@ -27,6 +29,7 @@ import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.resolve.DescriptorUtils
 import org.jetbrains.kotlin.resolve.scopes.MemberScope
 import org.jetbrains.kotlin.serialization.deserialization.findClassAcrossModuleDependencies
+import kotlin.jvm.internal.TypeIntrinsics
 import kotlin.reflect.*
 
 internal class KClassImpl<T : Any>(override val jClass: Class<T>) :
@@ -136,6 +139,14 @@ internal class KClassImpl<T : Any>(override val jClass: Class<T>) :
     override val objectInstance: T?
         get() = objectInstance_()
 
+    override fun isInstance(value: Any?): Boolean {
+        // TODO: use Kotlin semantics for mutable/read-only collections once KT-11754 is supported (see TypeIntrinsics)
+        jClass.functionClassArity?.let { arity ->
+            return TypeIntrinsics.isFunctionOfArity(value, arity)
+        }
+        return (jClass.wrapperByPrimitive ?: jClass).isInstance(value)
+    }
+
     override val typeParameters: List<KTypeParameter>
         get() = descriptor.declaredTypeParameters.map(::KTypeParameterImpl)