Scala Compiler2.13.18 < Back
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# 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 be a P, because it is an X [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 will 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
- Checkability
- InferCheckable

t

scala.tools.nsc.typechecker.Checkable

# InferCheckable

###

#### trait InferCheckable extends AnyRef

Self Type
  Analyzer.Inferencer
Source
  Checkable.scala

Linear Supertypes
AnyRef, Any
Known Subclasses
Inferencer
Type Hierarchy
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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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2. Show All

Visibility

1. Public
2. Protected

### 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 Analyzer.InferCheckable toany2stringadd[Analyzer.InferCheckable] performed by method any2stringadd in scala.Predef.
   Definition Classes
     any2stringadd
4.  def ->[B](y: B): (Analyzer.InferCheckable, B)
   Implicit
     This member is added by an implicit conversion from Analyzer.InferCheckable toArrowAssoc[Analyzer.InferCheckable] 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 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?

8.  def clone(): AnyRef
   Attributes
     protected[lang]
   Definition Classes
     AnyRef
   Annotations
     @throws(classOf[java.lang.CloneNotSupportedException]) @native()
9.  def ensuring(cond: (Analyzer.InferCheckable) => Boolean, msg: => Any): Analyzer.InferCheckable
   Implicit
     This member is added by an implicit conversion from Analyzer.InferCheckable toEnsuring[Analyzer.InferCheckable] performed by method Ensuring in scala.Predef.
   Definition Classes
     Ensuring
10.  def ensuring(cond: (Analyzer.InferCheckable) => Boolean): Analyzer.InferCheckable
    Implicit
      This member is added by an implicit conversion from Analyzer.InferCheckable toEnsuring[Analyzer.InferCheckable] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring
11.  def ensuring(cond: Boolean, msg: => Any): Analyzer.InferCheckable
    Implicit
      This member is added by an implicit conversion from Analyzer.InferCheckable toEnsuring[Analyzer.InferCheckable] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring
12.  def ensuring(cond: Boolean): Analyzer.InferCheckable
    Implicit
      This member is added by an implicit conversion from Analyzer.InferCheckable toEnsuring[Analyzer.InferCheckable] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring
13.  final def eq(arg0: AnyRef): Boolean
    Definition Classes
      AnyRef
14.  def equals(arg0: AnyRef): Boolean
    Definition Classes
      AnyRef → Any
15.  def finalize(): Unit
    Attributes
      protected[lang]
    Definition Classes
      AnyRef
    Annotations
      @throws(classOf[java.lang.Throwable])
16.  final def getClass(): Class[_ <: AnyRef]
    Definition Classes
      AnyRef → Any
    Annotations
      @native()
17.  def hashCode(): Int
    Definition Classes
      AnyRef → Any
    Annotations
      @native()
18.  def isCheckable(P0: Global.Type): Boolean
19.  final def isInstanceOf[T0]: Boolean
    Definition Classes
      Any
20.  def isUncheckable(P0: Global.Type): Boolean
21.  final def ne(arg0: AnyRef): Boolean
    Definition Classes
      AnyRef
22.  final def notify(): Unit
    Definition Classes
      AnyRef
    Annotations
      @native()
23.  final def notifyAll(): Unit
    Definition Classes
      AnyRef
    Annotations
      @native()
24.  final def synchronized[T0](arg0: => T0): T0
    Definition Classes
      AnyRef
25.  def toString(): String
    Definition Classes
      AnyRef → Any
26.  final def wait(): Unit
    Definition Classes
      AnyRef
    Annotations
      @throws(classOf[java.lang.InterruptedException])
27.  final def wait(arg0: Long, arg1: Int): Unit
    Definition Classes
      AnyRef
    Annotations
      @throws(classOf[java.lang.InterruptedException])
28.  final def wait(arg0: Long): Unit
    Definition Classes
      AnyRef
    Annotations
      @throws(classOf[java.lang.InterruptedException]) @native()

### Deprecated Value Members

1.  def formatted(fmtstr: String): String
   Implicit
     This member is added by an implicit conversion from Analyzer.InferCheckable toStringFormat[Analyzer.InferCheckable] 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.

2.  def →[B](y: B): (Analyzer.InferCheckable, B)
   Implicit
     This member is added by an implicit conversion from Analyzer.InferCheckable toArrowAssoc[Analyzer.InferCheckable] performed by method ArrowAssoc in scala.Predef.
   Definition Classes
     ArrowAssoc
   Annotations
     @deprecated
   Deprecated

     (Since version 2.13.0) Use `->` instead. If you still wish to display it as one character, consider using a font with programming ligatures such as Fira Code.

### Inherited from AnyRef

### Inherited from Any

### Inherited by implicit conversion any2stringadd fromAnalyzer.InferCheckable to any2stringadd[Analyzer.InferCheckable]

### Inherited by implicit conversion StringFormat fromAnalyzer.InferCheckable to StringFormat[Analyzer.InferCheckable]

### Inherited by implicit conversion Ensuring fromAnalyzer.InferCheckable to Ensuring[Analyzer.InferCheckable]

### Inherited by implicit conversion ArrowAssoc fromAnalyzer.InferCheckable to ArrowAssoc[Analyzer.InferCheckable]

### Ungrouped