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
  • trait PatternExpansion extends AnyRef

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

    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.
    Definition Classes
    patmat
  • ExtractorAlignment
  • ExtractorSubPatternAlignment
t

scala.tools.nsc.transform.patmat.PatternExpansion

ExtractorSubPatternAlignment

trait ExtractorSubPatternAlignment extends AnyRef

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

Source
PatternExpansion.scala
Linear Supertypes
AnyRef, Any
Known Subclasses
ExtractorCall, ExtractorCallProd, ExtractorCallRegular, ExtractorAlignment
Type Hierarchy
Ordering
  1. Alphabetic
  2. By Inheritance
Inherited
  1. ExtractorSubPatternAlignment
  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. Protected

Abstract Value Members

  1. abstract def args: List[Global.Tree]

    Args will be broken down into the concatenation of: productArity product patterns (fixed length, corresponding to fields in case class or tuple components in classic unapply, or product selectors in product-based unapply) elementArity element patterns (explicit patterns that pick off the prefix of the final sequence-valued component of the unapply, or a repeated case constructor arg) starArity star patterns (0 or 1, absorbs the remaining variable-length components)

Concrete Value Members

  1. val isStar: Boolean
  2. val nonStarArity: Int
  3. def starArity: Int
  4. def totalArity: Int