trait Checkable extends AnyRef

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.

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Checkable.scala
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Type Members

  1. trait InferCheckable extends AnyRef

Value Members

  1. final def !=(arg0: Any): Boolean
    Definition Classes
    AnyRef → Any
  2. final def ##(): Int
    Definition Classes
    AnyRef → Any
  3. def +(other: String): String
    Implicit
    This member is added by an implicit conversion from Checkable to any2stringadd[Checkable] performed by method any2stringadd in scala.Predef.
    Definition Classes
    any2stringadd
  4. def ->[B](y: B): (Checkable, B)
    Implicit
    This member is added by an implicit conversion from Checkable to ArrowAssoc[Checkable] performed by method ArrowAssoc in scala.Predef.
    Definition Classes
    ArrowAssoc
    Annotations
    @inline()
  5. final def ==(arg0: Any): Boolean
    Definition Classes
    AnyRef → Any
  6. final def asInstanceOf[T0]: T0
    Definition Classes
    Any
  7. def clone(): AnyRef
    Attributes
    protected[lang]
    Definition Classes
    AnyRef
    Annotations
    @throws( ... ) @native()
  8. def ensuring(cond: (Checkable) ⇒ Boolean, msg: ⇒ Any): Checkable
    Implicit
    This member is added by an implicit conversion from Checkable to Ensuring[Checkable] performed by method Ensuring in scala.Predef.
    Definition Classes
    Ensuring
  9. def ensuring(cond: (Checkable) ⇒ Boolean): Checkable
    Implicit
    This member is added by an implicit conversion from Checkable to Ensuring[Checkable] performed by method Ensuring in scala.Predef.
    Definition Classes
    Ensuring
  10. def ensuring(cond: Boolean, msg: ⇒ Any): Checkable
    Implicit
    This member is added by an implicit conversion from Checkable to Ensuring[Checkable] performed by method Ensuring in scala.Predef.
    Definition Classes
    Ensuring
  11. def ensuring(cond: Boolean): Checkable
    Implicit
    This member is added by an implicit conversion from Checkable to Ensuring[Checkable] performed by method Ensuring in scala.Predef.
    Definition Classes
    Ensuring
  12. final def eq(arg0: AnyRef): Boolean
    Definition Classes
    AnyRef
  13. def equals(arg0: Any): Boolean
    Definition Classes
    AnyRef → Any
  14. def finalize(): Unit
    Attributes
    protected[lang]
    Definition Classes
    AnyRef
    Annotations
    @throws( classOf[java.lang.Throwable] )
  15. final def getClass(): Class[_]
    Definition Classes
    AnyRef → Any
    Annotations
    @native()
  16. def hashCode(): Int
    Definition Classes
    AnyRef → Any
    Annotations
    @native()
  17. final def isInstanceOf[T0]: Boolean
    Definition Classes
    Any
  18. final def ne(arg0: AnyRef): Boolean
    Definition Classes
    AnyRef
  19. final def notify(): Unit
    Definition Classes
    AnyRef
    Annotations
    @native()
  20. final def notifyAll(): Unit
    Definition Classes
    AnyRef
    Annotations
    @native()
  21. def propagateKnownTypes(from: Global.Type, to: Global.Symbol): Global.Type

    The applied type of class 'to' after inferring anything possible from the knowledge that 'to' must also be of the type given in 'from'.

  22. final def synchronized[T0](arg0: ⇒ T0): T0
    Definition Classes
    AnyRef
  23. def toString(): String
    Definition Classes
    AnyRef → Any
  24. final def wait(): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws( ... )
  25. final def wait(arg0: Long, arg1: Int): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws( ... )
  26. final def wait(arg0: Long): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws( ... ) @native()
  27. def [B](y: B): (Checkable, B)
    Implicit
    This member is added by an implicit conversion from Checkable to ArrowAssoc[Checkable] performed by method ArrowAssoc in scala.Predef.
    Definition Classes
    ArrowAssoc

Deprecated Value Members

  1. def formatted(fmtstr: String): String
    Implicit
    This member is added by an implicit conversion from Checkable to StringFormat[Checkable] performed by method StringFormat in scala.Predef.
    Definition Classes
    StringFormat
    Annotations
    @deprecated @inline()
    Deprecated

    (Since version 2.12.16) Use formatString.format(value) instead of value.formatted(formatString), or use the f"" string interpolator. In Java 15 and later, formatted resolves to the new method in String which has reversed parameters.

Inherited from AnyRef

Inherited from Any

Inherited by implicit conversion any2stringadd from Checkable to any2stringadd[Checkable]

Inherited by implicit conversion StringFormat from Checkable to StringFormat[Checkable]

Inherited by implicit conversion Ensuring from Checkable to Ensuring[Checkable]

Inherited by implicit conversion ArrowAssoc from Checkable to ArrowAssoc[Checkable]

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