Scala Compiler2.12.21 < 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
- PatternExpansion
- PatternMatching
- PatternMatchingStats
- ScalaLogic
- Solving
- TreeAndTypeAnalysis

t

scala.tools.nsc.transform.patmat

# PatternExpansion 

###

#### trait PatternExpansion extends AnyRef

An 'extractor' can be a case class or an unapply or unapplySeq method.

In a case class, the class is the unextracted type and the fixed and repeated types are derived from its constructor parameters.

In an unapply, this is reversed: the parameter to the unapply is the unextracted type, and the other types are derived based on the return type of the unapply method.

An extractor returns: F1, F2, ..., Fi, opt[Seq[E] or E*] A case matches: P1, P2, ..., Pj, opt[Seq[E]] Put together: P1/F1, P2/F2, ... Pi/Fi, Pi+1/E, Pi+2/E, ... Pj/E, opt[Seq[E]]

Here Pm/Fi is the last pattern to match the fixed arity section.

productArity: the value of i, i.e. the number of non-sequence types in the extractor nonStarArity: the value of j, i.e. the number of non-star patterns in the case definition elementArity: j - i, i.e. the number of non-star patterns which must match sequence elements starArity: 1 or 0 based on whether there is a star (sequence-absorbing) pattern totalArity: nonStarArity + starArity, i.e. the number of patterns in the case definition

Note that productArity is a function only of the extractor, and nonStar/star/totalArity are all functions of the patterns. The key value for aligning and typing the patterns is elementArity, as it is derived from both sets of information.

If elementArity is...

- zero: A perfect match between extractor and the fixed patterns. If there is a star pattern it will match any sequence.
- positive: There are more patterns than products. There will have to be a sequence which can populate at least `elementArity` patterns.
- negative: There are more products than patterns: compile time error.

Source
  PatternExpansion.scala

Linear Supertypes
AnyRef, Any
Known Subclasses
patmat, PatternMatching
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Ordering

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2. By Inheritance

Inherited

1. PatternExpansion
2. AnyRef
3. 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.  class ExtractorAlignment extends ExtractorSubPatternAlignment
2.  trait ExtractorSubPatternAlignment extends AnyRef

   The arities we can derive looking only at the subpatterns (the args of the unapply node)

### Abstract Value Members

1.  abstract val global: Global

### 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
     This member is added by an implicit conversion from PatternExpansion to any2stringadd[PatternExpansion] performed by method any2stringadd in scala.Predef.
   Definition Classes
     any2stringadd
4.  def ->[B](y: B): (PatternExpansion, B)
   Implicit
     This member is added by an implicit conversion from PatternExpansion to ArrowAssoc[PatternExpansion] 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: (PatternExpansion) ⇒ Boolean, msg: ⇒ Any): PatternExpansion
   Implicit
     This member is added by an implicit conversion from PatternExpansion to Ensuring[PatternExpansion] performed by method Ensuring in scala.Predef.
   Definition Classes
     Ensuring
9.  def ensuring(cond: (PatternExpansion) ⇒ Boolean): PatternExpansion
   Implicit
     This member is added by an implicit conversion from PatternExpansion to Ensuring[PatternExpansion] performed by method Ensuring in scala.Predef.
   Definition Classes
     Ensuring
10.  def ensuring(cond: Boolean, msg: ⇒ Any): PatternExpansion
    Implicit
      This member is added by an implicit conversion from PatternExpansion to Ensuring[PatternExpansion] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring
11.  def ensuring(cond: Boolean): PatternExpansion
    Implicit
      This member is added by an implicit conversion from PatternExpansion to Ensuring[PatternExpansion] 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.  final def synchronized[T0](arg0: ⇒ T0): T0
    Definition Classes
      AnyRef
22.  def toString(): String
    Definition Classes
      AnyRef → Any
23.  def unapplyFormals(fun: Global.Tree, args: List[Global.Tree])(context: Context): List[Global.Type]
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): (PatternExpansion, B)
    Implicit
      This member is added by an implicit conversion from PatternExpansion to ArrowAssoc[PatternExpansion] 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 PatternExpansion to StringFormat[PatternExpansion] 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 PatternExpansion to any2stringadd[PatternExpansion]

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

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

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

### Ungrouped