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
-  trait MatchApproximation extends TreeAndTypeAnalysis with ScalaLogic with MatchTreeMaking
  Definition Classes
    patmat
- CODE
- CheckableTreeAndTypeAnalysis
- CodegenCore
- MatchApproximator
- MatchMonadInterface
- OptimizedCodegen
- PropositionalLogic
- PureCodegen
- PureMatchMonadInterface
- Suppression
- TreeMakers
- TreesAndTypesDomain
- TypedSubstitution
- debug
- vpmName

t

scala.tools.nsc.transform.patmat.MatchApproximation

# MatchApproximator 

###

#### 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)

Source
  MatchAnalysis.scala

Linear Supertypes
MatchApproximation.TreesAndTypesDomain, MatchApproximation.CheckableTreeAndTypeAnalysis, MatchApproximation.PropositionalLogic, MatchApproximation.TreeMakers, MatchApproximation.CodegenCore, MatchApproximation.TypedSubstitution, MatchApproximation.MatchMonadInterface, AnyRef, Any
Known Subclasses
MatchAnalyzer, CommonSubconditionElimination, MatchOptimizer, OptimizingMatchTranslator
 
Ordering

1. Alphabetic
2. By Inheritance

Inherited

1. MatchApproximator
2. TreesAndTypesDomain
3. CheckableTreeAndTypeAnalysis
4. PropositionalLogic
5. TreeMakers
6. CodegenCore
7. TypedSubstitution
8. MatchMonadInterface
9. AnyRef
10. 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 Substitution extends AnyRef
   Definition Classes
     TypedSubstitution
2.  trait AbsVar extends AnyRef
   Definition Classes
     PropositionalLogic
3.  final case class And(ops: Set[Prop]) extends Prop with Product with Serializable
   Definition Classes
     PropositionalLogic
4.  final case class AtMostOne(ops: List[Sym]) extends Prop with Product with Serializable
   Definition Classes
     PropositionalLogic
5.  final case class Eq(p: Var, q: Const) extends Prop with Product with Serializable
   Definition Classes
     PropositionalLogic
6.  final case class Not(a: Prop) extends Prop with Product with Serializable
   Definition Classes
     PropositionalLogic
7.  final case class Or(ops: Set[Prop]) extends Prop with Product with Serializable
   Definition Classes
     PropositionalLogic
8.  class Prop extends AnyRef
   Definition Classes
     PropositionalLogic
9.  trait PropMap extends AnyRef
   Definition Classes
     PropositionalLogic
10.  trait PropTraverser extends AnyRef
    Definition Classes
      PropositionalLogic
11.  final case class Solution(model: Model, unassigned: List[Sym]) extends Product with Serializable
    Definition Classes
      PropositionalLogic
12.  final class Sym extends Prop
    Definition Classes
      PropositionalLogic
13.  trait TypeConstExtractor extends AnyRef
    Definition Classes
      PropositionalLogic
14.  trait ValueConstExtractor extends AnyRef
    Definition Classes
      PropositionalLogic
15.  trait VarExtractor extends AnyRef
    Definition Classes
      PropositionalLogic
16.  type Model = Map[Sym, Boolean]
    Definition Classes
      PropositionalLogic
17.  abstract type Solvable
    Definition Classes
      PropositionalLogic
18.  case class Test(prop: MatchApproximator.Prop, treeMaker: MatchApproximator.TreeMaker) extends Product with Serializable
19.  type Tree = Global.Tree
    Definition Classes
      TreesAndTypesDomain → PropositionalLogic
20.  class TreeMakersToProps extends AnyRef
21.  type Type = Global.Type
    Definition Classes
      TreesAndTypesDomain → PropositionalLogic
22.  trait AbsCodegen extends AnyRef
    Definition Classes
      CodegenCore
23.  trait Casegen extends AbsCodegen
    Definition Classes
      CodegenCore
24.  abstract class CommonCodegen extends AbsCodegen
    Definition Classes
      CodegenCore
25.  case class AlternativesTreeMaker(prevBinder: Global.Symbol, altss: List[List[TreeMaker]], pos: Global.Position) extends TreeMaker with NoNewBinders with Product with Serializable
    Definition Classes
      TreeMakers
26.  case class BodyTreeMaker(body: Global.Tree, matchPt: Global.Type) extends TreeMaker with NoNewBinders with Product with Serializable
    Definition Classes
      TreeMakers
27.  sealed abstract class CondTreeMaker extends FunTreeMaker
    Definition Classes
      TreeMakers
28.  case class EqualityTestTreeMaker(prevBinder: Global.Symbol, patTree: Global.Tree, pos: Global.Position) extends CondTreeMaker with Product with Serializable
    Definition Classes
      TreeMakers
29.  case class ExtractorTreeMaker(extractor: Global.Tree, extraCond: Option[Global.Tree], nextBinder: Global.Symbol)(subPatBinders: List[Global.Symbol], subPatRefs: List[Global.Tree], potentiallyMutableBinders: Set[Global.Symbol], extractorReturnsBoolean: Boolean, checkedLength: Option[Int], prevBinder: Global.Symbol, ignoredSubPatBinders: Set[Global.Symbol]) extends FunTreeMaker with PreserveSubPatBinders with Product with Serializable

    Make a TreeMaker that will result in an extractor call specified by `extractor` the next TreeMaker (here, we don't know which it'll be) is chained after this one by flatMap'ing a function with binder `nextBinder` over our extractor's result the function's body is determined by the next TreeMaker (furthermore, the interpretation of `flatMap` depends on the codegen instance we're using).

    Make a TreeMaker that will result in an extractor call specified by `extractor` the next TreeMaker (here, we don't know which it'll be) is chained after this one by flatMap'ing a function with binder `nextBinder` over our extractor's result the function's body is determined by the next TreeMaker (furthermore, the interpretation of `flatMap` depends on the codegen instance we're using).

    The values for the subpatterns, as computed by the extractor call in `extractor`, are stored in local variables that re-use the symbols in `subPatBinders`. This makes extractor patterns more debuggable (scala/bug#5739).

    Definition Classes
      TreeMakers
30.  sealed abstract class FunTreeMaker extends TreeMaker
    Definition Classes
      TreeMakers
31.  case class GuardTreeMaker(guardTree: Global.Tree) extends TreeMaker with NoNewBinders with Product with Serializable
    Definition Classes
      TreeMakers
32.  sealed trait NoNewBinders extends TreeMaker
    Definition Classes
      TreeMakers
33.  sealed trait PreserveSubPatBinders extends TreeMaker
    Definition Classes
      TreeMakers
34.  case class ProductExtractorTreeMaker(prevBinder: Global.Symbol, extraCond: Option[Global.Tree])(subPatBinders: List[Global.Symbol], subPatRefs: List[Global.Tree], mutableBinders: List[Global.Symbol], binderKnownNonNull: Boolean, ignoredSubPatBinders: Set[Global.Symbol]) extends FunTreeMaker with PreserveSubPatBinders with Product with Serializable

    An optimized version of ExtractorTreeMaker for Products.

    An optimized version of ExtractorTreeMaker for Products. For now, this is hard-coded to case classes, and we simply extract the case class fields.

    The values for the subpatterns, as specified by the case class fields at the time of extraction, are stored in local variables that re-use the symbols in `subPatBinders`. This makes extractor patterns more debuggable (scala/bug#5739) as well as avoiding mutation after the pattern has been matched (scala/bug#5158, scala/bug#6070)

    TODO: make this user-definable as follows When a companion object defines a method `def unapply_1(x: T): U_1`, but no `def unapply` or `def unapplySeq`, the extractor is considered to match any non-null value of type T the pattern is expected to have as many sub-patterns as there are `def unapply_I(x: T): U_I` methods, and the type of the I'th sub-pattern is `U_I`. The same exception for Seq patterns applies: if the last extractor is of type `Seq[U_N]`, the pattern must have at least N arguments (exactly N if the last argument is annotated with `: _*`). The arguments starting at N (and beyond) are taken from the sequence returned by apply_N, and it is checked that that sequence has enough elements to provide values for all expected sub-patterns.

    For a case class C, the implementation is assumed to be `def unapply_I(x: C) = x._I`, and the extractor call is inlined under that assumption.

    Definition Classes
      TreeMakers
35.  case class SubstOnlyTreeMaker(prevBinder: Global.Symbol, nextBinder: Global.Symbol) extends TreeMaker with Product with Serializable
    Definition Classes
      TreeMakers
36.  abstract class TreeMaker extends AnyRef
    Definition Classes
      TreeMakers
37.  case class TrivialTreeMaker(tree: Global.Tree) extends TreeMaker with NoNewBinders with Product with Serializable
    Definition Classes
      TreeMakers
38.  case class TypeTestTreeMaker(prevBinder: Global.Symbol, testedBinder: Global.Symbol, expectedTp: Global.Type, nextBinderTp: Global.Type)(pos: Global.Position, extractorArgTypeTest: Boolean = false) extends CondTreeMaker with Product with Serializable

    implements the run-time aspects of (§8.2) (typedPattern has already done the necessary type transformations)

    implements the run-time aspects of (§8.2) (typedPattern has already done the necessary type transformations)

    Type patterns consist of types, type variables, and wildcards. A type pattern T is of one of the following forms:

    - A reference to a class C, p.C, or T#C. This type pattern matches any non-null instance of the given class. Note that the prefix of the class, if it is given, is relevant for determining class instances. For instance, the pattern p.C matches only instances of classes C which were created with the path p as prefix. The bottom types scala.Nothing and scala.Null cannot be used as type patterns, because they would match nothing in any case.
    - A singleton type p.type. This type pattern matches only the value denoted by the path p (that is, a pattern match involved a comparison of the matched value with p using method eq in class AnyRef). // TODO: the actual pattern matcher uses ==, so that's what I'm using for now // https://github.com/scala/bug/issues/4577 "pattern matcher, still disappointing us at equality time"
    - A compound type pattern T1 with ... with Tn where each Ti is a type pat- tern. This type pattern matches all values that are matched by each of the type patterns Ti.
    - A parameterized type pattern T[a1,...,an], where the ai are type variable patterns or wildcards _. This type pattern matches all values which match T for some arbitrary instantiation of the type variables and wildcards. The bounds or alias type of these type variable are determined as described in (§8.3).
    - A parameterized type pattern scala.Array[T1], where T1 is a type pattern. // TODO This type pattern matches any non-null instance of type scala.Array[U1], where U1 is a type matched by T1.
    Definition Classes
      TreeMakers
39.  sealed abstract class Const extends AnyRef
    Definition Classes
      TreesAndTypesDomain
40.  sealed class TypeConst extends Const
    Definition Classes
      TreesAndTypesDomain
41.  sealed class ValueConst extends Const
    Definition Classes
      TreesAndTypesDomain
42.  class Var extends AbsVar
    Definition Classes
      TreesAndTypesDomain

### Abstract Value Members

1.  abstract val EmptyModel: Model
   Definition Classes
     PropositionalLogic
2.  abstract val NoModel: Model
   Definition Classes
     PropositionalLogic
3.  abstract def analyzeCases(prevBinder: Global.Symbol, cases: List[List[TreeMaker]], pt: Global.Type, suppression: MatchApproximation.Suppression): Unit
   Definition Classes
     TreeMakers
4.  abstract def codegen: AbsCodegen
   Definition Classes
     CodegenCore
5.  abstract def eqFreePropToSolvable(f: Prop): Solvable
   Definition Classes
     PropositionalLogic
6.  abstract def findAllModelsFor(solvable: Solvable, sym: Global.Symbol = NoSymbol): List[Solution]
   Definition Classes
     PropositionalLogic
7.  abstract def findModelFor(solvable: Solvable): Model
   Definition Classes
     PropositionalLogic
8.  abstract def optimizeCases(prevBinder: Global.Symbol, cases: List[List[TreeMaker]], pt: Global.Type, selectorPos: Global.Position): (List[List[TreeMaker]], List[Global.Tree])
   Definition Classes
     TreeMakers
9.  abstract def reportWarning(message: String): Unit
   Definition Classes
     PropositionalLogic
10.  abstract val typer: (analyzer)#Typer
    Definition Classes
      CheckableTreeAndTypeAnalysis
11.  abstract def uncheckedWarning(pos: Global.Position, msg: String, site: Global.Symbol): Unit
    Definition Classes
      PropositionalLogic

### Concrete Value Members

1.  object EmptySubstitution extends Substitution
   Definition Classes
     TypedSubstitution
2.  object Substitution
   Definition Classes
     TypedSubstitution
3.  object AnalysisBudget
   Definition Classes
     PropositionalLogic
4.  object And extends Serializable
   Definition Classes
     PropositionalLogic
5.  object False extends Prop with Product with Serializable
   Definition Classes
     PropositionalLogic
6.  object Or extends Serializable
   Definition Classes
     PropositionalLogic
7.  object Sym
   Definition Classes
     PropositionalLogic
8.  object True extends Prop with Product with Serializable
   Definition Classes
     PropositionalLogic
9.  final def !=(arg0: Any): Boolean
   Definition Classes
     AnyRef → Any
10.  final def ##(): Int
    Definition Classes
      AnyRef → Any
11.  def +(other: String): String
    Implicit
      This member is added by an implicit conversion from MatchApproximator to any2stringadd[MatchApproximator] performed by method any2stringadd in scala.Predef.
    Definition Classes
      any2stringadd
12.  def ->[B](y: B): (MatchApproximator, B)
    Implicit
      This member is added by an implicit conversion from MatchApproximator to ArrowAssoc[MatchApproximator] performed by method ArrowAssoc in scala.Predef.
    Definition Classes
      ArrowAssoc
    Annotations
      @inline()
13.  def /\(props: Iterable[Prop]): Product with Serializable with Prop
    Definition Classes
      PropositionalLogic
14.  final def ==(arg0: Any): Boolean
    Definition Classes
      AnyRef → Any
15.  def \/(props: Iterable[Prop]): Product with Serializable with Prop
    Definition Classes
      PropositionalLogic
16.  def approximateMatchConservative(root: Global.Symbol, cases: List[List[TreeMaker]]): List[List[Test]]
17.  final def asInstanceOf[T0]: T0
    Definition Classes
      Any
18.  val budgetProp: sys.Prop[String]
    Definition Classes
      PropositionalLogic
19.  final def caseWithoutBodyToProp(tests: List[Test]): Prop
    Attributes
      protected
20.  def checkableType(tp: Global.Type): Global.Type
    Definition Classes
      CheckableTreeAndTypeAnalysis
21.  def clone(): AnyRef
    Attributes
      protected[lang]
    Definition Classes
      AnyRef
    Annotations
      @throws( ... ) @native()
22.  def combineCases(scrut: Global.Tree, scrutSym: Global.Symbol, casesRaw: List[List[TreeMaker]], pt: Global.Type, selectorPos: Global.Position, owner: Global.Symbol, matchFailGenOverride: Option[(Global.Tree) ⇒ Global.Tree]): Global.Tree
    Definition Classes
      TreeMakers
23.  def combineCasesNoSubstOnly(scrut: Global.Tree, scrutSym: Global.Symbol, casesNoSubstOnly: List[List[TreeMaker]], pt: Global.Type, selectorPos: Global.Position, owner: Global.Symbol, matchFailGenOverride: Option[(Global.Tree) ⇒ Global.Tree]): Global.Tree
    Definition Classes
      TreeMakers
24.  def combineExtractors(treeMakers: List[TreeMaker])(casegen: Casegen): Global.Tree
    Definition Classes
      TreeMakers
25.  val debugInfoEmitVars: Boolean
    Attributes
      protected
    Definition Classes
      TreeMakers
26.  def emitSwitch(scrut: Global.Tree, scrutSym: Global.Symbol, cases: List[List[TreeMaker]], pt: Global.Type, matchFailGenOverride: Option[(Global.Tree) ⇒ Global.Tree], unchecked: Boolean): Option[Global.Tree]
    Definition Classes
      TreeMakers
27.  def emitTypeSwitch(bindersAndCases: List[(Global.Symbol, List[TreeMaker])], pt: Global.Type): Option[List[Global.CaseDef]]
    Definition Classes
      TreeMakers
28.  def ensuring(cond: (MatchApproximator) ⇒ Boolean, msg: ⇒ Any): MatchApproximator
    Implicit
      This member is added by an implicit conversion from MatchApproximator to Ensuring[MatchApproximator] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring
29.  def ensuring(cond: (MatchApproximator) ⇒ Boolean): MatchApproximator
    Implicit
      This member is added by an implicit conversion from MatchApproximator to Ensuring[MatchApproximator] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring
30.  def ensuring(cond: Boolean, msg: ⇒ Any): MatchApproximator
    Implicit
      This member is added by an implicit conversion from MatchApproximator to Ensuring[MatchApproximator] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring
31.  def ensuring(cond: Boolean): MatchApproximator
    Implicit
      This member is added by an implicit conversion from MatchApproximator to Ensuring[MatchApproximator] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring
32.  def enumerateSubtypes(tp: Global.Type, grouped: Boolean): List[List[Global.Type]]
    Definition Classes
      CheckableTreeAndTypeAnalysis
33.  final def eq(arg0: AnyRef): Boolean
    Definition Classes
      AnyRef
34.  def equals(arg0: Any): Boolean
    Definition Classes
      AnyRef → Any
35.  def finalize(): Unit
    Attributes
      protected[lang]
    Definition Classes
      AnyRef
    Annotations
      @throws( classOf[java.lang.Throwable] )
36.  def fixerUpper(origOwner: Global.Symbol, pos: Global.Position): Global.Traverser
    Attributes
      protected
    Definition Classes
      TreeMakers
37.  def freshName(prefix: String): Global.TermName
    Definition Classes
      CodegenCore
38.  def freshSym(pos: Global.Position, tp: Global.Type = NoType, prefix: String = "x"): Global.TermSymbol
    Definition Classes
      CodegenCore
39.  def gatherSymbols(p: Prop): Set[Sym]
    Definition Classes
      PropositionalLogic
40.  def gatherVariables(p: Prop): Set[Var]
    Definition Classes
      PropositionalLogic
41.  final def getClass(): Class[_]
    Definition Classes
      AnyRef → Any
    Annotations
      @native()
42.  def hashCode(): Int
    Definition Classes
      AnyRef → Any
    Annotations
      @native()
43.  final def isInstanceOf[T0]: Boolean
    Definition Classes
      Any
44.  val matchOwner: Global.Symbol
    Definition Classes
      MatchMonadInterface
45.  final def ne(arg0: AnyRef): Boolean
    Definition Classes
      AnyRef
46.  def newSynthCaseLabel(name: String): Global.MethodSymbol
    Definition Classes
      CodegenCore
47.  final def notify(): Unit
    Definition Classes
      AnyRef
    Annotations
      @native()
48.  final def notifyAll(): Unit
    Definition Classes
      AnyRef
    Annotations
      @native()
49.  def prepareNewAnalysis(): Unit
    Definition Classes
      TreesAndTypesDomain → PropositionalLogic
50.  def propToSolvable(p: Prop): Solvable
    Definition Classes
      PropositionalLogic
51.  def propagateSubstitution(treeMakers: List[TreeMaker], initial: Substitution): List[TreeMaker]
    Definition Classes
      TreeMakers
52.  def pureType(tp: Global.Type): Global.Type
    Definition Classes
      MatchMonadInterface
53.  def removeSubstOnly(makers: List[TreeMaker]): collection.immutable.List[TreeMaker]
    Definition Classes
      TreeMakers
54.  def removeVarEq(props: List[Prop], modelNull: Boolean = false): (Prop, List[Prop])
    Definition Classes
      PropositionalLogic
55.  def reportMissingCases(pos: Global.Position, counterExamples: List[String]): Unit
    Definition Classes
      MatchMonadInterface
56.  def reportUnreachable(pos: Global.Position): Unit
    Definition Classes
      MatchMonadInterface
57.  def showTreeMakers(cases: List[List[TreeMaker]]): Unit
58.  def simplify(f: Prop): Prop

    Simplifies propositional formula according to the following rules: - eliminate double negation (avoids unnecessary Tseitin variables) - flatten trees of same connectives (avoids unnecessary Tseitin variables) - removes constants and connectives that are in fact constant because of their operands - eliminates duplicate operands - convert formula into NNF: all sub-expressions have a positive polarity which makes them amenable for the subsequent Plaisted transformation and increases chances to figure out that the formula is already in CNF

    Simplifies propositional formula according to the following rules: - eliminate double negation (avoids unnecessary Tseitin variables) - flatten trees of same connectives (avoids unnecessary Tseitin variables) - removes constants and connectives that are in fact constant because of their operands - eliminates duplicate operands - convert formula into NNF: all sub-expressions have a positive polarity which makes them amenable for the subsequent Plaisted transformation and increases chances to figure out that the formula is already in CNF

    Complexity: DFS over formula tree

    See http://www.decision-procedures.org/slides/propositional_logic-2x3.pdf

    Definition Classes
      PropositionalLogic
59.  final def synchronized[T0](arg0: ⇒ T0): T0
    Definition Classes
      AnyRef
60.  def toString(): String
    Definition Classes
      AnyRef → Any
61.  def uncheckableType(tp: Global.Type): Boolean
    Definition Classes
      CheckableTreeAndTypeAnalysis
62.  final def wait(): Unit
    Definition Classes
      AnyRef
    Annotations
      @throws( ... )
63.  final def wait(arg0: Long, arg1: Int): Unit
    Definition Classes
      AnyRef
    Annotations
      @throws( ... )
64.  final def wait(arg0: Long): Unit
    Definition Classes
      AnyRef
    Annotations
      @throws( ... ) @native()
65.  def →[B](y: B): (MatchApproximator, B)
    Implicit
      This member is added by an implicit conversion from MatchApproximator to ArrowAssoc[MatchApproximator] performed by method ArrowAssoc in scala.Predef.
    Definition Classes
      ArrowAssoc
66.  object Test extends Serializable
67.  object IrrefutableExtractorTreeMaker
    Definition Classes
      TreeMakers
68.  object TypeTestTreeMaker extends Serializable
    Definition Classes
      TreeMakers
69.  object Const
    Definition Classes
      TreesAndTypesDomain
70.  object NullConst extends Const with Product with Serializable
    Definition Classes
      TreesAndTypesDomain → PropositionalLogic
71.  object TypeConst extends TypeConstExtractor
    Definition Classes
      TreesAndTypesDomain → PropositionalLogic
72.  object ValueConst extends ValueConstExtractor
    Definition Classes
      TreesAndTypesDomain → PropositionalLogic
73.  object Var extends VarExtractor
    Definition Classes
      TreesAndTypesDomain → PropositionalLogic

### Deprecated Value Members

1.  def formatted(fmtstr: String): String
   Implicit
     This member is added by an implicit conversion from MatchApproximator to StringFormat[MatchApproximator] 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 MatchApproximation.TreesAndTypesDomain

### Inherited from MatchApproximation.CheckableTreeAndTypeAnalysis

### Inherited from MatchApproximation.PropositionalLogic

### Inherited from MatchApproximation.TreeMakers

### Inherited from MatchApproximation.CodegenCore

### Inherited from MatchApproximation.TypedSubstitution

### Inherited from MatchApproximation.MatchMonadInterface

### Inherited from AnyRef

### Inherited from Any

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

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

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

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

### Ungrouped