Packages

  • package root

    The Scala compiler and reflection APIs.

    The Scala compiler and reflection APIs.

    Definition Classes
    root
  • package scala
    Definition Classes
    root
  • package tools
    Definition Classes
    scala
  • package nsc
    Definition Classes
    tools
  • package typechecker
    Definition Classes
    nsc
  • trait Checkable extends AnyRef

    On pattern matcher checkability:

    On pattern matcher checkability:

    The spec says that case _: List[Int] should be always issue an unchecked warning:

    > Types which are not of one of the forms described above are > also accepted as type patterns. However, such type patterns > will be translated to their erasure (§3.7). The Scala compiler > will issue an “unchecked” warning for these patterns to flag > the possible loss of type-safety.

    But the implementation goes a little further to omit warnings based on the static type of the scrutinee. As a trivial example:

    def foo(s: Seq[Int]) = s match { case _: List[Int] => }

    need not issue this warning.

    Consider a pattern match of this form: (x: X) match { case _: P => }

    There are four possibilities to consider: [P1] X will always conform to P [P2] x will never conform to P [P3] X will conform to P if some runtime test is true [P4] X cannot be checked against P

    The first two cases correspond to those when there is enough static information to say X <: P or that (x ∈ X) ⇒ (x ∉ P). The fourth case includes unknown abstract types or structural refinements appearing within a pattern.

    The third case is the interesting one. We designate another type, XR, which is essentially the intersection of X and |P|, where |P| is the erasure of P. If XR <: P, then no warning is emitted.

    We evaluate "X with conform to P" by checking X <: P_wild, where P_wild is the result of substituting wildcard types in place of pattern type variables. This is intentionally stricter than (X matchesPattern P), see scala/bug#8597 for motivating test cases.

    Examples of how this info is put to use: sealed trait A[T] ; class B[T] extends A[T] def f(x: B[Int]) = x match { case _: A[Int] if true => } def g(x: A[Int]) = x match { case _: B[Int] => }

    f requires no warning because X=B[Int], P=A[Int], and B[Int] <:< A[Int]. g requires no warning because X=A[Int], P=B[Int], XR=B[Int], and B[Int] <:< B[Int]. XR=B[Int] because a value of type A[Int] which is tested to be a B can only be a B[Int], due to the definition of B (B[T] extends A[T].)

    This is something like asSeenFrom, only rather than asking what a type looks like from the point of view of one of its base classes, we ask what it looks like from the point of view of one of its subclasses.

    Definition Classes
    typechecker
  • InferCheckable

trait InferCheckable extends AnyRef

Self Type
Analyzer.Inferencer
Source
Checkable.scala
Linear Supertypes
AnyRef, Any
Known Subclasses
Inferencer
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Inherited
  1. InferCheckable
  2. AnyRef
  3. Any
Implicitly
  1. by any2stringadd
  2. by StringFormat
  3. by Ensuring
  4. by ArrowAssoc
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Visibility
  1. Public
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Value Members

  1. def checkCheckable(tree: Global.Tree, P0: Global.Type, X0: Global.Type, inPattern: Boolean, canRemedy: Boolean = false): Unit

    TODO: much better error positions.

    TODO: much better error positions. Kind of stuck right now because they just pass us the one tree. TODO: Eliminate inPattern, canRemedy, which have no place here.

    Instead of the canRemedy flag, annotate uncheckable types that have become checkable because of the availability of a class tag?

  2. def isCheckable(P0: Global.Type): Boolean
  3. def isUncheckable(P0: Global.Type): Boolean