Question

case class Test(kind: Int) {
  val ifX = if (isX) "is X" else "not X"
  val isX = kind == 1
}

val test = Test(1)
println("ifX=%s, isX=%b".format(test.ifX, test.isX))

Why this code print:
ifX=not X, isX=true

When is move “val ifX” before “ifX” it’s ok (print ifX=is X)

EDIT: I know how to fix that. I can’t understand why compiler not issue warning or error in this situation.

Answer 1

You are making the assumption that order doesn’t matter in scala. It does. Because isX is a variable value, and while it’s defined when ifX runs, it’s value is still uninitialized, and so it is the default for its type (boolean, so false).

If you redefine isX as a function (def isX = ...) it would work.

This is roughly equivalent to the following Java:

class Test {
    String ifX;
    bool isX; // Defaults to false, its a primitive after all
    public Test(Int kind) {
        ifX = isX ? "is X" : "not X";
        isX = kind == 1;
    }
}