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

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
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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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### Type Members

1. #### implicit class AlignedOps extends AnyRef

   Definition Classes
     ScalacPatternExpanders

2. #### trait CNF extends PropositionalLogic

   Definition Classes
     Solving

3. #### trait CheckableTreeAndTypeAnalysis extends AnyRef

   Definition Classes
     TreeAndTypeAnalysis

4. #### trait CodegenCore extends MatchMonadInterface

   Definition Classes
     MatchCodeGen

5. #### trait CommonSubconditionElimination extends OptimizedCodegen with MatchApproximator

   Definition Classes
     MatchOptimization

6. #### trait MatchAnalyzer extends MatchApproximator

   Definition Classes
     MatchAnalysis

7. #### 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)

8. #### 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:

9. #### trait MatchOptimizer extends OptimizedCodegen with SwitchEmission with CommonSubconditionElimination

   Definition Classes
     MatchOptimization

10. #### class MatchTransformer extends TypingTransformer

11. #### trait MatchTranslator extends PatternMatching.TreeMakers with PatternMatching.TreeMakerWarnings

    Definition Classes
      MatchTranslation

12. #### trait OptimizedCodegen extends CodegenCore with TypedSubstitution with MatchMonadInterface

    Definition Classes
      MatchCodeGen

13. #### class OptimizingMatchTranslator extends MatchTranslator with MatchOptimizer with MatchAnalyzer with Solver

14. #### type PatternAligned = ScalacPatternExpanders.ScalacPatternExpander.Aligned

    Definition Classes
      ScalacPatternExpanders

15. #### class Phase extends StdPhase

    The phase defined by this transform

16. #### trait PropositionalLogic extends AnyRef

    Definition Classes
      Logic

17. #### trait PureCodegen extends CodegenCore with PureMatchMonadInterface

    Definition Classes
      MatchCodeGen

18. #### trait PureMatchMonadInterface extends MatchMonadInterface

    Definition Classes
      MatchCodeGen

19. #### class PureMatchTranslator extends MatchTranslator with PureCodegen

20. #### trait ScalacPatternExpander extends PatternExpander[Global.Tree, Global.Type]

    Definition Classes
      ScalacPatternExpanders

21. #### trait Solver extends CNF

    Definition Classes
      Solving

22. #### abstract class StdPhase extends GlobalPhase

    A standard phase template

23. #### final case class Suppression(exhaustive: Boolean, unreachable: Boolean) extends Product with Serializable

    Definition Classes
      MatchTreeMaking

24. #### trait SwitchEmission extends TreeMakers with MatchMonadInterface

    Definition Classes
      MatchOptimization

25. #### trait TreeMakerWarnings extends AnyRef

    Definition Classes
      MatchWarnings

26. #### trait TreeMakers extends TypedSubstitution with CodegenCore

    Definition Classes
      MatchTreeMaking

27. #### trait TreesAndTypesDomain extends PropositionalLogic with CheckableTreeAndTypeAnalysis

    Definition Classes
      ScalaLogic

28. #### trait TypedSubstitution extends MatchMonadInterface

    Definition Classes
      Interface

29. #### abstract class TypingTransformer extends Global.Transformer

    Definition Classes
      TypingTransformers

### 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. #### final def !=(arg0: Any): Boolean

   Definition Classes
     AnyRef → Any

2. #### final def ##(): Int

   Definition Classes
     AnyRef → Any

3. #### def +(other: String): String

   Implicit information
     This member is added by an implicit conversion from PatternMatching to any2stringadd[PatternMatching] performed by method any2stringadd in scala.Predef.
   Definition Classes
     any2stringadd

4. #### def ->[B](y: B): (PatternMatching, B)

   Implicit information
     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()

5. #### final def ==(arg0: Any): Boolean

   Definition Classes
     AnyRef → Any

6. #### object CODE

   Definition Classes
     TreeDSL

7. #### object Suppression extends Serializable

   Definition Classes
     MatchTreeMaking

8. #### final def afterOwnPhase[T](op: ⇒ T): T

   Definition Classes
     SubComponent
   Annotations
     @inline()

9. #### def alignAcrossRows(xss: List[List[AnyRef]], sep: String, lineSep: String = "\n"): String

   Definition Classes
     Logic

10. #### object alignPatterns extends ScalacPatternExpander

    Definition Classes
      ScalacPatternExpanders

11. #### final def asInstanceOf[T0]: T0

    Definition Classes
      Any

12. #### final def beforeOwnPhase[T](op: ⇒ T): T

    Definition Classes
      SubComponent
    Annotations
      @inline()

13. #### 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

14. #### def clone(): AnyRef

    Attributes
      protected[java.lang]
    Definition Classes
      AnyRef
    Annotations
      @throws( ... )

15. #### final def dealiasWiden(tp: Global.Type): Global.Type

    Attributes
      protected
    Definition Classes
      Interface

16. #### object debug

    Definition Classes
      Debugging

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 information
      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 information
      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 information
      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 information
      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 finalize(): Unit

    Attributes
      protected[java.lang]
    Definition Classes
      AnyRef
    Annotations
      @throws( classOf[java.lang.Throwable] )

25. #### def formatted(fmtstr: String): String

    Implicit information
      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()

26. #### final def getClass(): Class[_]

    Definition Classes
      AnyRef → Any

27. #### final def hasStableSymbol(p: Global.Tree): Boolean

    Attributes
      protected
    Definition Classes
      Interface

28. #### 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

29. #### 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

30. #### def instanceOfTpImplies(tp: Global.Type, tpImplied: Global.Type): Boolean

    Definition Classes
      TreeAndTypeAnalysis

31. #### 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

32. #### final def isInstanceOf[T0]: Boolean

    Definition Classes
      Any

33. #### final def mkFALSE: Global.Literal

    Attributes
      protected
    Definition Classes
      Interface

34. #### final def mkTRUE: Global.Literal

    Attributes
      protected
    Definition Classes
      Interface

35. #### final def ne(arg0: AnyRef): Boolean

    Definition Classes
      AnyRef

36. #### def newPhase(prev: nsc.Phase): StdPhase

    Create a new phase which applies transformer

    Create a new phase which applies transformer

    Definition Classes
      Transform → SubComponent

37. #### def newTransformer(unit: Global.CompilationUnit): Global.Transformer

    The transformer factory

    The transformer factory

    Definition Classes
      PatternMatching → Transform

38. #### final def notify(): Unit

    Definition Classes
      AnyRef

39. #### final def notifyAll(): Unit

    Definition Classes
      AnyRef

40. #### 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

41. #### val phaseName: String

    The name of the phase

    The name of the phase

    Definition Classes
      PatternMatching → SubComponent

42. #### 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

43. #### 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

44. #### def removeCPSFromPt(pt: Global.Type): Global.Type

    Definition Classes
      MatchCps

45. #### val requires: List[String]

    Names of phases required by this component.

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

    Definition Classes
      SubComponent

46. #### 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

47. #### def sameValue(a: Global.Tree, b: Global.Tree): Boolean

    Definition Classes
      TreeAndTypeAnalysis

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. #### object vpmName

    Definition Classes
      Interface

52. #### final def wait(): Unit

    Definition Classes
      AnyRef
    Annotations
      @throws( ... )

53. #### final def wait(arg0: Long, arg1: Int): Unit

    Definition Classes
      AnyRef
    Annotations
      @throws( ... )

54. #### final def wait(arg0: Long): Unit

    Definition Classes
      AnyRef
    Annotations
      @throws( ... )

55. #### def →[B](y: B): (PatternMatching, B)

    Implicit information
      This member is added by an implicit conversion from PatternMatching to ArrowAssoc[PatternMatching] performed by method ArrowAssoc in scala.Predef.
    Definition Classes
      ArrowAssoc

### 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