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

Known Subclasses

patmat

Type Hierarchy

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Inherited

PatternMatching
ScalacPatternExpanders
MatchWarnings
MatchOptimization
MatchAnalysis
MatchApproximation
Solving
ScalaLogic
TreeAndTypeAnalysis
Logic
MatchCps
MatchTreeMaking
MatchCodeGen
MatchTranslation
Interface
TreeDSL
Debugging
TypingTransformers
Transform
SubComponent
AnyRef
Any

Implicitly

by any2stringadd
by StringFormat
by Ensuring
by ArrowAssoc

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Type Members

abstract class StdPhase extends GlobalPhase
A standard phase template
A standard phase template

Definition Classes
SubComponent
class Phase extends StdPhase
The phase defined by this transform
The phase defined by this transform

Definition Classes
Transform
abstract class TypingTransformer extends Global.Transformer

Definition Classes
TypingTransformers

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:

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

trait TypedSubstitution extends MatchMonadInterface

Definition Classes
Interface
trait PropositionalLogic extends AnyRef

Definition Classes
Logic
trait MatchAnalyzer extends MatchApproximator

Definition Classes
MatchAnalysis
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
trait CodegenCore extends MatchMonadInterface

Definition Classes
MatchCodeGen
trait OptimizedCodegen extends CodegenCore with TypedSubstitution with MatchMonadInterface

Definition Classes
MatchCodeGen
trait PureCodegen extends CodegenCore with PureMatchMonadInterface

Definition Classes
MatchCodeGen
trait PureMatchMonadInterface extends MatchMonadInterface

Definition Classes
MatchCodeGen
trait CommonSubconditionElimination extends OptimizedCodegen with MatchApproximator

Definition Classes
MatchOptimization
trait MatchOptimizer extends OptimizedCodegen with SwitchEmission with CommonSubconditionElimination

Definition Classes
MatchOptimization
trait SwitchEmission extends TreeMakers with MatchMonadInterface

Definition Classes
MatchOptimization
trait MatchTranslator extends PatternMatching.TreeMakers with PatternMatching.TreeMakerWarnings

Definition Classes
MatchTranslation
final case class Suppression (suppressExhaustive: Boolean, suppressUnreachable: Boolean) extends Product with Serializable

Definition Classes
MatchTreeMaking
trait TreeMakers extends TypedSubstitution with CodegenCore

Definition Classes
MatchTreeMaking
trait TreeMakerWarnings extends AnyRef

Definition Classes
MatchWarnings
class MatchTransformer extends TypingTransformer
class OptimizingMatchTranslator extends MatchTranslator with MatchOptimizer with MatchAnalyzer with Solver
type PatternAligned = ScalacPatternExpanders.ScalacPatternExpander.Aligned

Definition Classes
ScalacPatternExpanders
class PureMatchTranslator extends MatchTranslator with PureCodegen
trait TreesAndTypesDomain extends PropositionalLogic with CheckableTreeAndTypeAnalysis

Definition Classes
ScalaLogic
implicit class AlignedOps extends AnyRef

Definition Classes
ScalacPatternExpanders
trait ScalacPatternExpander extends PatternExpander[Global.Tree, Global.Type]

Definition Classes
ScalacPatternExpanders
trait CNF extends PropositionalLogic

Definition Classes
Solving
trait Solver extends CNF

Definition Classes
Solving
trait CheckableTreeAndTypeAnalysis extends AnyRef

Definition Classes
TreeAndTypeAnalysis

Abstract Value Members

abstract val global: Global

Definition Classes
ScalacPatternExpanders
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
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

object CODE

Definition Classes
TreeDSL
object debug

Definition Classes
Debugging
object vpmName

Definition Classes
Interface
object Suppression extends Serializable

Definition Classes
MatchTreeMaking
final def !=(arg0: Any): Boolean
Test two objects for inequality.
Test two objects for inequality.
returns
true if !(this == that), false otherwise.

Definition Classes
AnyRef → Any
final def ##(): Int
Equivalent to x.hashCode except for boxed numeric types and null.
Equivalent to x.hashCode except for boxed numeric types and null. For numerics, it returns a hash value which is consistent with value equality: if two value type instances compare as true, then ## will produce the same hash value for each of them. For null returns a hashcode where null.hashCode throws a NullPointerException.
returns
a hash value consistent with ==

Definition Classes
AnyRef → Any
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
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()
final def ==(arg0: Any): Boolean
The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).
The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).
returns
true if the receiver object is equivalent to the argument; false otherwise.

Definition Classes
AnyRef → Any
final def afterOwnPhase[T](op: ⇒ T): T

Definition Classes
SubComponent
Annotations
@inline()
def alignAcrossRows(xss: List[List[Any]], sep: String, lineSep: String = "\n"): String

Definition Classes
Logic
final def asInstanceOf[T0]: T0
Cast the receiver object to be of type T0.
Cast the receiver object to be of type T0.
Note that the success of a cast at runtime is modulo Scala's erasure semantics. Therefore the expression 1.asInstanceOf[String] will throw a ClassCastException at runtime, while the expression List(1).asInstanceOf[List[String]] will not. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the requested type.
returns
the receiver object.

Definition Classes
Any
Exceptions thrown
ClassCastException if the receiver object is not an instance of the erasure of type T0.
final def beforeOwnPhase[T](op: ⇒ T): T

Definition Classes
SubComponent
Annotations
@inline()
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
def clone(): AnyRef
Create a copy of the receiver object.
Create a copy of the receiver object.
The default implementation of the clone method is platform dependent.
returns
a copy of the receiver object.

Attributes
protected[java.lang]
Definition Classes
AnyRef
Annotations
@throws( ... )
Note
not specified by SLS as a member of AnyRef
final def dealiasWiden(tp: Global.Type): Global.Type

Attributes
protected
Definition Classes
Interface
def enabled: Boolean
Is this component enabled? Default is true.
Is this component enabled? Default is true.

Definition Classes
SubComponent
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
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
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
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
final def eq(arg0: AnyRef): Boolean
Tests whether the argument (that) is a reference to the receiver object (this).
Tests whether the argument (that) is a reference to the receiver object (this).
The eq method implements an equivalence relation on non-null instances of AnyRef, and has three additional properties:
- It is consistent: for any non-null instances x and y of type AnyRef, multiple invocations of x.eq(y) consistently returns true or consistently returns false.
- For any non-null instance x of type AnyRef, x.eq(null) and null.eq(x) returns false.
- null.eq(null) returns true.
When overriding the equals or hashCode methods, it is important to ensure that their behavior is consistent with reference equality. Therefore, if two objects are references to each other (o1 eq o2), they should be equal to each other (o1 == o2) and they should hash to the same value (o1.hashCode == o2.hashCode).
returns
true if the argument is a reference to the receiver object; false otherwise.

Definition Classes
AnyRef
def equals(arg0: Any): Boolean
The equality method for reference types.
The equality method for reference types. Default implementation delegates to eq.
See also equals in scala.Any.
returns
true if the receiver object is equivalent to the argument; false otherwise.

Definition Classes
AnyRef → Any
def equivalentTree(a: Global.Tree, b: Global.Tree): Boolean

Definition Classes
TreeAndTypeAnalysis
def finalize(): Unit
Called by the garbage collector on the receiver object when there are no more references to the object.
Called by the garbage collector on the receiver object when there are no more references to the object.
The details of when and if the finalize method is invoked, as well as the interaction between finalize and non-local returns and exceptions, are all platform dependent.

Attributes
protected[java.lang]
Definition Classes
AnyRef
Annotations
@throws( classOf[java.lang.Throwable] )
Note
not specified by SLS as a member of AnyRef
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()
final def getClass(): Class[_]
Returns the runtime class representation of the object.
Returns the runtime class representation of the object.
returns
a class object corresponding to the runtime type of the receiver.

Definition Classes
AnyRef → Any
final def hasStableSymbol(p: Global.Tree): Boolean

Attributes
protected
Definition Classes
Interface
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
returns
the hash code value for this object.

Definition Classes
SubComponent → AnyRef → Any
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
def instanceOfTpImplies(tp: Global.Type, tpImplied: Global.Type): Boolean

Definition Classes
TreeAndTypeAnalysis
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
final def isInstanceOf[T0]: Boolean
Test whether the dynamic type of the receiver object is T0.
Test whether the dynamic type of the receiver object is T0.
Note that the result of the test is modulo Scala's erasure semantics. Therefore the expression 1.isInstanceOf[String] will return false, while the expression List(1).isInstanceOf[List[String]] will return true. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the specified type.
returns
true if the receiver object is an instance of erasure of type T0; false otherwise.

Definition Classes
Any
final def mkFALSE: Global.Literal

Attributes
protected
Definition Classes
Interface
final def mkTRUE: Global.Literal

Attributes
protected
Definition Classes
Interface
final def ne(arg0: AnyRef): Boolean
Equivalent to !(this eq that).
Equivalent to !(this eq that).
returns
true if the argument is not a reference to the receiver object; false otherwise.

Definition Classes
AnyRef
def newPhase(prev: nsc.Phase): StdPhase
Create a new phase which applies transformer
Create a new phase which applies transformer

Definition Classes
Transform → SubComponent
def newTransformer(unit: Global.CompilationUnit): Global.Transformer
The transformer factory
The transformer factory

Definition Classes
PatternMatching → Transform
final def notify(): Unit
Wakes up a single thread that is waiting on the receiver object's monitor.
Wakes up a single thread that is waiting on the receiver object's monitor.

Definition Classes
AnyRef
Note
not specified by SLS as a member of AnyRef
final def notifyAll(): Unit
Wakes up all threads that are waiting on the receiver object's monitor.
Wakes up all threads that are waiting on the receiver object's monitor.

Definition Classes
AnyRef
Note
not specified by SLS as a member of AnyRef
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
val phaseName: String
The name of the phase
The name of the phase

Definition Classes
PatternMatching → SubComponent
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
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
def removeCPSFromPt(pt: Global.Type): Global.Type

Definition Classes
MatchCps
val requires: List[String]
Names of phases required by this component.
Names of phases required by this component. Default is Nil.

Definition Classes
SubComponent
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
final def synchronized[T0](arg0: ⇒ T0): T0

Definition Classes
AnyRef
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
def toString(): String
Creates a String representation of this object.
Creates a String representation of this object. The default representation is platform dependent. On the java platform it is the concatenation of the class name, "@", and the object's hashcode in hexadecimal.
returns
a String representation of the object.

Definition Classes
AnyRef → Any
final def wait(): Unit

Definition Classes
AnyRef
Annotations
@throws( ... )
final def wait(arg0: Long, arg1: Int): Unit

Definition Classes
AnyRef
Annotations
@throws( ... )
final def wait(arg0: Long): Unit

Definition Classes
AnyRef
Annotations
@throws( ... )
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
object alignPatterns extends ScalacPatternExpander

Definition Classes
ScalacPatternExpanders

Packages

PatternMatching

Type Members

Abstract Value Members

Concrete Value Members

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

Packages

PatternMatching 

Type Members

Abstract Value Members

Concrete Value Members

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

PatternMatching