init

Widen the abstract value of the argument so that its height is below the specified height.

It can be used to mark method or constructor arguments, as the following example shows:

class A(x: Int): def square(): Int = x*x

class C(val a: A)

object B: val a = build(new C(new A(10)): @widen(2)) // <-- usage

 def build(c: C) = new A(c.a.square())           // calling methods on parameter

By default, method and constructor arguments are widened to height 1. In the code above, without using @widen(2) we will have the abstract value C(a = Cold) for the argument c of the method build. Consequently, the checker will issue a warning for the method call c.a.square() because it is forbidden to call methods or access fields on cold values.

Introduce a region context.

The same mutable field in the same region have the same abstract representation.

The concept of regions is intended to make context-sensitivity tunable for complex use cases.

Example:

trait B { def foo(): Int }
class C(var x: Int) extends B { def foo(): Int = 20 }
class D(var y: Int) extends B { def foo(): Int = A.m }
class Box(var value: B)

 object A:
   val box1: Box = region { new Box(new C(5))  }
   val box2: Box = region { new Box(new D(10)) }
   val m: Int = box1.value.foo()

In the above, without the two region annotations, the two objects box1 and box2 are in the same region. Therefore, the field box1.value and box2.value points to both instances of C and D. Consequently, the method call box1.value.foo() will be invalid, because it reaches A.m, which is not yet initialized. The explicit context annotation solves the problem.