scala.tools.nsc.transform.patmat
PatternMatching
Related Doc:
package patmat
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)
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:
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)) }
The phase defined by this transform
The phase defined by this transform
A standard phase template
A standard phase template
Names of phases that must run before this phase.
Names of phases that must run before this phase.
Name of the phase that this phase must follow immediately.
Name of the phase that this phase must follow immediately.
Test two objects for inequality.
Test two objects for inequality.
true if !(this == that), false otherwise.
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.
a hash value consistent with ==
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).
true if the receiver object is equivalent to the argument; false otherwise.
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.
the receiver object.
ClassCastException if the receiver object is not an instance of the erasure of type T0.
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.
Create a copy of the receiver object.
Create a copy of the receiver object.
The default implementation of the clone method is platform dependent.
a copy of the receiver object.
not specified by SLS as a member of AnyRef
Is this component enabled? Default is true.
Is this component enabled? Default is true.
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:
x and y of type AnyRef, multiple invocations of
x.eq(y) consistently returns true or consistently returns false.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).
true if the argument is a reference to the receiver object; false otherwise.
The equality method for reference types.
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.
not specified by SLS as a member of AnyRef
A representation that corresponds to the dynamic class of the receiver object.
A representation that corresponds to the dynamic class of the receiver object.
The nature of the representation is platform dependent.
a representation that corresponds to the dynamic class of the receiver object.
not specified by SLS as a member of AnyRef
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
the hash code value for this object.
True if this phase runs before all other phases.
True if this phase runs before all other phases. Usually, parser.
True if this phase is not provided by a plug-in.
True if this phase is not provided by a plug-in.
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.
true if the receiver object is an instance of erasure of type T0; false otherwise.
Equivalent to !(this eq that).
Equivalent to !(this eq that).
true if the argument is not a reference to the receiver object; false otherwise.
Create a new phase which applies transformer
Create a new phase which applies transformer
The transformer factory
The transformer factory
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.
not specified by SLS as a member of AnyRef
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.
not specified by SLS as a member of AnyRef
The phase corresponding to this subcomponent in the current compiler run
The phase corresponding to this subcomponent in the current compiler run
The name of the phase
The name of the phase
New flags defined by the phase which are not valid before
New flags defined by the phase which are not valid before
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
Names of phases required by this component.
Names of phases required by this component. Default is Nil.
Names of phases that must run after this phase.
Names of phases that must run after this phase. Default is Nil.
True if this phase runs after all other phases.
True if this phase runs after all other phases. Usually, terminal.
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.
a String representation of the object.
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 usingone).Cases are combined into a pattern match using the
orElsecombinator (the implicit failure case is expressed using the monad'szero).TODO:
(longer-term) TODO: