scala.tools.nsc.transform.patmat.PatternMatching
PureMatchTranslator
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package PatternMatching
scala.tools.nsc.transform.patmat.PatternMatching
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 (SI-5739).
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 (SI-5739) as well as
avoiding mutation after the pattern has been matched (SI-5158, SI-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.
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:
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.
A conservative approximation of which patterns do not discern anything.
A conservative approximation of which patterns do not discern anything. They are discarded during the translation.
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.
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
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
The hashCode method for reference types.
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.
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
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.
The translation of pat if guard => body has two aspects:
1) the substitution due to the variables bound by patterns
2) the combination of the extractor calls using flatMap.
The translation of pat if guard => body has two aspects:
1) the substitution due to the variables bound by patterns
2) the combination of the extractor calls using flatMap.
2) is easy -- it looks like: translatePattern_1.flatMap(translatePattern_2....flatMap(translatePattern_N.flatMap(translateGuard.flatMap((x_i) => success(Xbody(x_i)))))...)
this must be right-leaning tree, as can be seen intuitively by considering the scope of bound variables:
variables bound by pat_1 must be visible from the function inside the left-most flatMap right up to Xbody all the way on the right
1) is tricky because translatePattern_i determines the shape of translatePattern_i+1:
zoom in on translatePattern_1.flatMap(translatePattern_2) for example -- it actually looks more like:
translatePattern_1(x_scrut).flatMap((x_1) => {y_i -> x_1._i}translatePattern_2)
x_1 references the result (inside the monad) of the extractor corresponding to pat_1,
this result holds the values for the constructor arguments, which translatePattern_1 has extracted
from the object pointed to by x_scrut. The y_i are the symbols bound by pat_1 (in order)
in the scope of the remainder of the pattern, and they must thus be replaced by:
x_1in the treemakers,
Thus, the result type of translatePattern_i's extractor must conform to M[(T_1,..., T_n)].
Operationally, phase 1) is a foldLeft, since we must consider the depth-first-flattening of the transformed patterns from left to right. For every pattern ast node, it produces a transformed ast and a function that will take care of binding and substitution of the next ast (to the right).
Implement a pattern match by turning its cases (including the implicit failure case)
into the corresponding (monadic) extractors, and combining them with the orElse combinator.
Implement a pattern match by turning its cases (including the implicit failure case)
into the corresponding (monadic) extractors, and combining them with the orElse combinator.
For scrutinee match { case1 ... caseN }, the resulting tree has the shape
runOrElse(scrutinee)(x => translateCase1(x).orElse(translateCase2(x)).....orElse(zero))
NOTE: the resulting tree is not type checked, nor are nested pattern matches transformed thus, you must typecheck the result (and that will in turn translate nested matches) this could probably optimized... (but note that the matchStrategy must be solved for each nested patternmatch)