Scala Compiler2.12.2-20170504-135222-21d12e9 < 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 transform
  Definition Classes
    nsc
-  package patmat
  Definition Classes
    transform
- Debugging
- Interface
- Lit
- Logic
- MatchAnalysis
- MatchApproximation
- MatchCodeGen
- MatchCps
- MatchOptimization
- MatchTranslation
- MatchTreeMaking
- MatchWarnings
- PatternExpander
- PatternMatching
- PatternMatchingStats
- ScalaLogic
- ScalacPatternExpanders
- Solving
- TreeAndTypeAnalysis

t

scala.tools.nsc.transform.patmat

# PatternMatching 

###

#### trait PatternMatching extends SubComponent with Transform with TypingTransformers with Debugging with Interface with MatchTranslation with MatchTreeMaking with MatchCodeGen with MatchCps with ScalaLogic with Solving with MatchAnalysis with MatchOptimization with MatchWarnings with ScalacPatternExpanders

Translate pattern matching.

Either into optimized if/then/else's, or virtualized as method calls (these methods form a zero-plus monad), similar in spirit to how for-comprehensions are compiled.

For each case, express all patterns as extractor calls, guards as 0-ary extractors, and sequence them using `flatMap` (lifting the body of the case into the monad using `one`).

Cases are combined into a pattern match using the `orElse` combinator (the implicit failure case is expressed using the monad's `zero`).

TODO:

- DCE (on irrefutable patterns)
- update spec and double check it's implemented correctly (see TODO's)

(longer-term) TODO:

- user-defined unapplyProd
- recover GADT typing by locally inserting implicit witnesses to type equalities derived from the current case, and considering these witnesses during subtyping (?)
- recover exhaustivity/unreachability of user-defined extractors by partitioning the types they match on using an HList or similar type-level structure

Source
  PatternMatching.scala

Linear Supertypes
ScalacPatternExpanders, MatchWarnings, MatchOptimization, MatchAnalysis, MatchApproximation, Solving, ScalaLogic, TreeAndTypeAnalysis, Logic, MatchCps, MatchTreeMaking, MatchCodeGen, MatchTranslation, Interface, TreeDSL, Debugging, TypingTransformers, Transform, SubComponent, AnyRef, Any
Known Subclasses
patmat
Type Hierarchy
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Ordering

1. Alphabetic
2. By Inheritance

Inherited

1. PatternMatching
2. ScalacPatternExpanders
3. MatchWarnings
4. MatchOptimization
5. MatchAnalysis
6. MatchApproximation
7. Solving
8. ScalaLogic
9. TreeAndTypeAnalysis
10. Logic
11. MatchCps
12. MatchTreeMaking
13. MatchCodeGen
14. MatchTranslation
15. Interface
16. TreeDSL
17. Debugging
18. TypingTransformers
19. Transform
20. SubComponent
21. AnyRef
22. Any

Implicitly

1. by any2stringadd
2. by StringFormat
3. by Ensuring
4. by ArrowAssoc

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Visibility

1. Public
2. All

### Type Members

1.  abstract class StdPhase extends GlobalPhase

   A standard phase template

   A standard phase template

   Definition Classes
     SubComponent
2.  class Phase extends StdPhase

   The phase defined by this transform

   The phase defined by this transform

   Definition Classes
     Transform
3.  abstract class TypingTransformer extends Global.Transformer
   Definition Classes
     TypingTransformers
4.  trait MatchMonadInterface extends AnyRef

   Interface with user-defined match monad? if there's a `__match` in scope, we use this as the match strategy, assuming it conforms to MatchStrategy as defined below:

   Interface with user-defined match monad? if there's a `__match` in scope, we use this as the match strategy, assuming it conforms to MatchStrategy as defined below:

       type Matcher[P[_], M[+_], A] = {
         def flatMap[B](f: P[A] => M[B]): M[B]
         def orElse[B >: A](alternative: => M[B]): M[B]
       }

       abstract class MatchStrategy[P[_], M[+_]] {
         // runs the matcher on the given input
         def runOrElse[T, U](in: P[T])(matcher: P[T] => M[U]): P[U]

         def zero: M[Nothing]
         def one[T](x: P[T]): M[T]
         def guard[T](cond: P[Boolean], then: => P[T]): M[T]
       }

   P and M are derived from one's signature (`def one[T](x: P[T]): M[T]`)

   if no `__match` is found, we assume the following implementation (and generate optimized code accordingly)

       object __match extends MatchStrategy[({type Id[x] = x})#Id, Option] {
         def zero = None
         def one[T](x: T) = Some(x)
         // NOTE: guard's return type must be of the shape M[T], where M is the monad in which the pattern match should be interpreted
         def guard[T](cond: Boolean, then: => T): Option[T] = if(cond) Some(then) else None
         def runOrElse[T, U](x: T)(f: T => Option[U]): U = f(x) getOrElse (throw new MatchError(x))
       }

   Definition Classes
     Interface
5.  trait TypedSubstitution extends MatchMonadInterface
   Definition Classes
     Interface
6.  trait PropositionalLogic extends AnyRef
   Definition Classes
     Logic
7.  trait MatchAnalyzer extends MatchApproximator
   Definition Classes
     MatchAnalysis
8.  trait MatchApproximator extends TreeMakers with TreesAndTypesDomain

   Represent a match as a formula in propositional logic that encodes whether the match matches (abstractly: we only consider types)

   Represent a match as a formula in propositional logic that encodes whether the match matches (abstractly: we only consider types)

   Definition Classes
     MatchApproximation
9.  trait CodegenCore extends MatchMonadInterface
   Definition Classes
     MatchCodeGen
10.  trait OptimizedCodegen extends CodegenCore with TypedSubstitution with MatchMonadInterface
    Definition Classes
      MatchCodeGen
11.  trait PureCodegen extends CodegenCore with PureMatchMonadInterface
    Definition Classes
      MatchCodeGen
12.  trait PureMatchMonadInterface extends MatchMonadInterface
    Definition Classes
      MatchCodeGen
13.  trait CommonSubconditionElimination extends OptimizedCodegen with MatchApproximator
    Definition Classes
      MatchOptimization
14.  trait MatchOptimizer extends OptimizedCodegen with SwitchEmission with CommonSubconditionElimination
    Definition Classes
      MatchOptimization
15.  trait SwitchEmission extends TreeMakers with MatchMonadInterface
    Definition Classes
      MatchOptimization
16.  trait MatchTranslator extends PatternMatching.TreeMakers with PatternMatching.TreeMakerWarnings
    Definition Classes
      MatchTranslation
17.  final case class Suppression (suppressExhaustive: Boolean, suppressUnreachable: Boolean) extends Product with Serializable
    Definition Classes
      MatchTreeMaking
18.  trait TreeMakers extends TypedSubstitution with CodegenCore
    Definition Classes
      MatchTreeMaking
19.  trait TreeMakerWarnings extends AnyRef
    Definition Classes
      MatchWarnings
20.  class MatchTransformer extends TypingTransformer
21.  class OptimizingMatchTranslator extends MatchTranslator with MatchOptimizer with MatchAnalyzer with Solver
22.  type PatternAligned = ScalacPatternExpanders.ScalacPatternExpander.Aligned
    Definition Classes
      ScalacPatternExpanders
23.  class PureMatchTranslator extends MatchTranslator with PureCodegen
24.  trait TreesAndTypesDomain extends PropositionalLogic with CheckableTreeAndTypeAnalysis
    Definition Classes
      ScalaLogic
25.  implicit class AlignedOps extends AnyRef
    Definition Classes
      ScalacPatternExpanders
26.  trait ScalacPatternExpander extends PatternExpander[Global.Tree, Global.Type]
    Definition Classes
      ScalacPatternExpanders
27.  trait CNF extends PropositionalLogic
    Definition Classes
      Solving
28.  trait Solver extends CNF
    Definition Classes
      Solving
29.  trait CheckableTreeAndTypeAnalysis extends AnyRef
    Definition Classes
      TreeAndTypeAnalysis

### Abstract Value Members

1.  abstract val global: Global
   Definition Classes
     ScalacPatternExpanders
2.  abstract val runsAfter: List[String]

   Names of phases that must run before this phase.

   Names of phases that must run before this phase.

   Definition Classes
     SubComponent
3.  abstract val runsRightAfter: Option[String]

   Name of the phase that this phase must follow immediately.

   Name of the phase that this phase must follow immediately.

   Definition Classes
     SubComponent

### Concrete Value Members

1.  object CODE
   Definition Classes
     TreeDSL
2.  object debug
   Definition Classes
     Debugging
3.  object vpmName
   Definition Classes
     Interface
4.  object Suppression extends Serializable
   Definition Classes
     MatchTreeMaking
5.  final def !=(arg0: Any): Boolean
   Definition Classes
     AnyRef → Any
6.  final def ##(): Int
   Definition Classes
     AnyRef → Any
7.  def +(other: String): String
   Implicit
     This member is added by an implicit conversion from PatternMatching to any2stringadd[PatternMatching] performed by method any2stringadd in scala.Predef.
   Definition Classes
     any2stringadd
8.  def ->[B](y: B): (PatternMatching, B)
   Implicit
     This member is added by an implicit conversion from PatternMatching to ArrowAssoc[PatternMatching] performed by method ArrowAssoc in scala.Predef.
   Definition Classes
     ArrowAssoc
   Annotations
     @inline()
9.  final def ==(arg0: Any): Boolean
   Definition Classes
     AnyRef → Any
10.  final def afterOwnPhase[T](op: ⇒ T): T
    Definition Classes
      SubComponent
    Annotations
      @inline()
11.  def alignAcrossRows(xss: List[List[Any]], sep: String, lineSep: String = "\n"): String
    Definition Classes
      Logic
12.  final def asInstanceOf[T0]: T0
    Definition Classes
      Any
13.  final def beforeOwnPhase[T](op: ⇒ T): T
    Definition Classes
      SubComponent
    Annotations
      @inline()
14.  def binderTypeImpliedByPattern(pat: Global.Tree, pt: Global.Type, binder: Global.Symbol): Global.Type

    Compute the type T implied for a value `v` matched by a pattern `pat` (with expected type `pt`).

    Compute the type T implied for a value `v` matched by a pattern `pat` (with expected type `pt`).

    Usually, this is the pattern's type because pattern matching implies instance-of checks.

    However, Stable Identifier and Literal patterns are matched using `==`, which does not imply a type for the binder that binds the matched value.

    See SI-1503, SI-5024: don't cast binders to types we're not sure they have

    TODO: update spec as follows (deviation between `**`):

    A pattern binder x@p consists of a pattern variable x and a pattern p. The type of the variable x is the static type T **IMPLIED BY** the pattern p. This pattern matches any value v matched by the pattern p **Deleted: , provided the run-time type of v is also an instance of T, ** and it binds the variable name to that value.

    Addition: A pattern `p` _implies_ a type `T` if the pattern matches only values of the type `T`.

    Definition Classes
      TreeAndTypeAnalysis
15.  def clone(): AnyRef
    Attributes
      protected[java.lang]
    Definition Classes
      AnyRef
    Annotations
      @throws( ... )
16.  final def dealiasWiden(tp: Global.Type): Global.Type
    Attributes
      protected
    Definition Classes
      Interface
17.  def enabled: Boolean

    Is this component enabled? Default is true.

    Is this component enabled? Default is true.

    Definition Classes
      SubComponent
18.  def ensuring(cond: (PatternMatching) ⇒ Boolean, msg: ⇒ Any): PatternMatching
    Implicit
      This member is added by an implicit conversion from PatternMatching to Ensuring[PatternMatching] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring
19.  def ensuring(cond: (PatternMatching) ⇒ Boolean): PatternMatching
    Implicit
      This member is added by an implicit conversion from PatternMatching to Ensuring[PatternMatching] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring
20.  def ensuring(cond: Boolean, msg: ⇒ Any): PatternMatching
    Implicit
      This member is added by an implicit conversion from PatternMatching to Ensuring[PatternMatching] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring
21.  def ensuring(cond: Boolean): PatternMatching
    Implicit
      This member is added by an implicit conversion from PatternMatching to Ensuring[PatternMatching] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring
22.  final def eq(arg0: AnyRef): Boolean
    Definition Classes
      AnyRef
23.  def equals(arg0: Any): Boolean
    Definition Classes
      AnyRef → Any
24.  def equivalentTree(a: Global.Tree, b: Global.Tree): Boolean
    Definition Classes
      TreeAndTypeAnalysis
25.  def finalize(): Unit
    Attributes
      protected[java.lang]
    Definition Classes
      AnyRef
    Annotations
      @throws( classOf[java.lang.Throwable] )
26.  def formatted(fmtstr: String): String
    Implicit
      This member is added by an implicit conversion from PatternMatching to StringFormat[PatternMatching] performed by method StringFormat in scala.Predef.
    Definition Classes
      StringFormat
    Annotations
      @inline()
27.  final def getClass(): Class[_]
    Definition Classes
      AnyRef → Any
28.  final def hasStableSymbol(p: Global.Tree): Boolean
    Attributes
      protected
    Definition Classes
      Interface
29.  def hashCode(): Int

    SubComponent are added to a HashSet and two phases are the same if they have the same name

    SubComponent are added to a HashSet and two phases are the same if they have the same name

    Definition Classes
      SubComponent → AnyRef → Any
30.  val initial: Boolean

    True if this phase runs before all other phases.

    True if this phase runs before all other phases. Usually, `parser`.

    Definition Classes
      SubComponent
31.  def instanceOfTpImplies(tp: Global.Type, tpImplied: Global.Type): Boolean
    Definition Classes
      TreeAndTypeAnalysis
32.  val internal: Boolean

    True if this phase is not provided by a plug-in.

    True if this phase is not provided by a plug-in.

    Definition Classes
      SubComponent
33.  final def isInstanceOf[T0]: Boolean
    Definition Classes
      Any
34.  final def mkFALSE: Global.Literal
    Attributes
      protected
    Definition Classes
      Interface
35.  final def mkTRUE: Global.Literal
    Attributes
      protected
    Definition Classes
      Interface
36.  final def ne(arg0: AnyRef): Boolean
    Definition Classes
      AnyRef
37.  def newPhase(prev: nsc.Phase): StdPhase

    Create a new phase which applies transformer

    Create a new phase which applies transformer

    Definition Classes
      Transform → SubComponent
38.  def newTransformer(unit: Global.CompilationUnit): Global.Transformer

    The transformer factory

    The transformer factory

    Definition Classes
      PatternMatching → Transform
39.  final def notify(): Unit
    Definition Classes
      AnyRef
40.  final def notifyAll(): Unit
    Definition Classes
      AnyRef
41.  def ownPhase: nsc.Phase

    The phase corresponding to this subcomponent in the current compiler run

    The phase corresponding to this subcomponent in the current compiler run

    Definition Classes
      SubComponent
42.  val phaseName: String

    The name of the phase

    The name of the phase

    Definition Classes
      PatternMatching → SubComponent
43.  def phaseNewFlags: Long

    New flags defined by the phase which are not valid before

    New flags defined by the phase which are not valid before

    Definition Classes
      SubComponent
44.  def phaseNextFlags: Long

    New flags defined by the phase which are not valid until immediately after it

    New flags defined by the phase which are not valid until immediately after it

    Definition Classes
      SubComponent
45.  def removeCPSFromPt(pt: Global.Type): Global.Type
    Definition Classes
      MatchCps
46.  val requires: List[String]

    Names of phases required by this component.

    Names of phases required by this component. Default is `Nil`.

    Definition Classes
      SubComponent
47.  val runsBefore: List[String]

    Names of phases that must run after this phase.

    Names of phases that must run after this phase. Default is `Nil`.

    Definition Classes
      SubComponent
48.  final def synchronized[T0](arg0: ⇒ T0): T0
    Definition Classes
      AnyRef
49.  val terminal: Boolean

    True if this phase runs after all other phases.

    True if this phase runs after all other phases. Usually, `terminal`.

    Definition Classes
      SubComponent
50.  def toString(): String
    Definition Classes
      AnyRef → Any
51.  final def wait(): Unit
    Definition Classes
      AnyRef
    Annotations
      @throws( ... )
52.  final def wait(arg0: Long, arg1: Int): Unit
    Definition Classes
      AnyRef
    Annotations
      @throws( ... )
53.  final def wait(arg0: Long): Unit
    Definition Classes
      AnyRef
    Annotations
      @throws( ... )
54.  def →[B](y: B): (PatternMatching, B)
    Implicit
      This member is added by an implicit conversion from PatternMatching to ArrowAssoc[PatternMatching] performed by method ArrowAssoc in scala.Predef.
    Definition Classes
      ArrowAssoc
55.  object alignPatterns extends ScalacPatternExpander
    Definition Classes
      ScalacPatternExpanders

### Inherited from ScalacPatternExpanders

### Inherited from MatchWarnings

### Inherited from MatchOptimization

### Inherited from MatchAnalysis

### Inherited from MatchApproximation

### Inherited from Solving

### Inherited from ScalaLogic

### Inherited from TreeAndTypeAnalysis

### Inherited from Logic

### Inherited from MatchCps

### Inherited from MatchTreeMaking

### Inherited from MatchCodeGen

### Inherited from MatchTranslation

### Inherited from Interface

### Inherited from TreeDSL

### Inherited from Debugging

### Inherited from TypingTransformers

### Inherited from Transform

### Inherited from SubComponent

### Inherited from AnyRef

### Inherited from Any

### Inherited by implicit conversion any2stringadd from PatternMatching to any2stringadd[PatternMatching]

### Inherited by implicit conversion StringFormat from PatternMatching to StringFormat[PatternMatching]

### Inherited by implicit conversion Ensuring from PatternMatching to Ensuring[PatternMatching]

### Inherited by implicit conversion ArrowAssoc from PatternMatching to ArrowAssoc[PatternMatching]

### Ungrouped