Scala中Stream中的“类”和“案例类”有什么区别？

Question

class A(x: Int)
def f(a: A): Stream[A] = a #:: f(new A(a.x + 1))

case class B(x: Int)
def f(b: B): Stream[B] = b #:: f(B(b.x + 1))

I expected these two cases would do the same action. But the former failed with an error(value x is not member of A). Why does only the former fail?

Answer 1

A case class has its constructor parameters automatically made into accessible fields. For example, your class B has x as a field and so Bx is legal. Your class A is not a case class and so its x was not made into an accessible field. If you want a non-case class to have its constructor parameters accessible they must be explicitly marked with val :

class A(val x: Int)