Any differences between asInstanceOf[X] and toX for value types?

Question

I used IntelliJ\'s ability to convert Java code to Scala code which generally works quite well.

It seems that IntelliJ replaced all casts with calls to asInstanceO

Answer 1

I do not know of any such cases. You can check yourself that the emitted bytecode is the same by compiling a class like

class Conv {
  def b(i: Int) = i.toByte
  def B(i: Int) = i.asInstanceOf[Byte]
  def s(i: Int) = i.toShort
  def S(i: Int) = i.asInstanceOf[Short]
  def f(i: Int) = i.toFloat 
  def F(i: Int) = i.asInstanceOf[Float]  
  def d(i: Int) = i.toDouble
  def D(i: Int) = i.asInstanceOf[Double]
}

and using javap -c Conv to get

public byte b(int);
  Code:
   0:   iload_1
   1:   i2b
   2:   ireturn

public byte B(int);
  Code:
   0:   iload_1
   1:   i2b
   2:   ireturn

...

where you can see that the exact same bytecode is emitted in each case.

Answer 2

Well, toInt and toLong are not casts. The correct conversion of type casting is asInstanceOf indeed. For example:

scala> val x: Any = 5
x: Any = 5

scala> if (x.isInstanceOf[Int]) x.asInstanceOf[Int] + 1
res6: AnyVal = 6

scala> if (x.isInstanceOf[Int]) x.toInt + 1
<console>:8: error: value toInt is not a member of Any
       if (x.isInstanceOf[Int]) x.toInt + 1
                                  ^