Why doesn't Kotlin perform automatic type-casting?

Question

var a : Double
a = Math.sin(10) // error: the integer literal does not conform to the expected type Double
a = Math.sin(10.0) //This compiles successfully
println(a)         


        

Answer 1

We all know that Kotlin has both non-nullable Int and nullable Int?.

When we use Int? this happens: Kotlin actually 'boxes' JVM primitives when Kotlin needs a nullable reference since it's aimed at eliminating the danger of null references from code.

Now look at this: (assuming this is a compilable code)

val a: Int? = 1
val b: Long? = a

Kotlin doesn't perform implicit type conversion because of this thing happens. If Kotlin did implicit type conversions, b should be 1. but since a is a boxed Int and b is a boxed Long, a == b yields false and falls into contradiction, since its == operator checks for equals() and Long's equals() checks other part to be Long as well.

Check the documentation:

• Explicit Conversions in Kotlin
• https://kotlinlang.org/docs/reference/basic-types.html
• https://kotlinlang.org/docs/reference/equality.html