Why MyClass::class.java.simpleName can't be constant value?

user_3752013 0
Viewed 311

A normal val is OK, and is initialized.

class MyClass {
    companion object {
        private val TAG = MyClass::class.java.simpleName
    }
}

But const val causes compilation error.

class MyClass {
    companion object {
        private const val TAG = MyClass::class.java.simpleName
    }
}

error log

MyClass.kt:27:33: error: const 'val' initializer should be a constant value
        private const val TAG = MyClass::class.java.simpleName

It seems unintuitive that simpleName cannot be defined as a const val.

kotlin
3 Answers

Reflection is a language's ability to inspect and dynamically call classes, methods, attributes, etc. at runtime.

Reflections can't be used at compile-time, they are only available at the runtime, so you can't use either of ::class or ::class.java, they won't be available at the compile-time.

The const modifier marks the val a compile-time constant. Hence can't call any runtime functions at compile-time.

user_113771120

In Kotlin, the const keyword should only be used when the value is a compile-time constant. Here MyClass::class.java.simpleName is not a compile-time constant. so we need to use val instead of const. val is same as the final keyword in Java.

For more info on this, please check here

user_32699580

const keyword is used to define compile-time constants but val can have runtime constants. simplename is not available at compile time hence the error.

user_53705690
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