trait Checkable extends AnyRef
On pattern matcher checkability:
The spec says that case _: List[Int] should be always issue an unchecked warning:
> Types which are not of one of the forms described above are > also accepted as type patterns. However, such type patterns > will be translated to their erasure (§3.7). The Scala compiler > will issue an “unchecked” warning for these patterns to flag > the possible loss of type-safety.
But the implementation goes a little further to omit warnings based on the static type of the scrutinee. As a trivial example:
def foo(s: Seq[Int]) = s match { case _: List[Int] => }
need not issue this warning.
Consider a pattern match of this form: (x: X) match { case _: P => }
There are four possibilities to consider: [P1] X will always conform to P [P2] x will never conform to P [P3] X will conform to P if some runtime test is true [P4] X cannot be checked against P
The first two cases correspond to those when there is enough static information to say X <: P or that (x ∈ X) ⇒ (x ∉ P). The fourth case includes unknown abstract types or structural refinements appearing within a pattern.
The third case is the interesting one. We designate another type, XR, which is essentially the intersection of X and |P|, where |P| is the erasure of P. If XR <: P, then no warning is emitted.
We evaluate "X with conform to P" by checking X <: P_wild, where
P_wild is the result of substituting wildcard types in place of
pattern type variables. This is intentionally stricter than
(X matchesPattern P), see SI-8597 for motivating test cases.
Examples of how this info is put to use: sealed trait A[T] ; class B[T] extends A[T] def f(x: B[Int]) = x match { case _: A[Int] if true => } def g(x: A[Int]) = x match { case _: B[Int] => }
f requires no warning because X=B[Int], P=A[Int], and B[Int] <:< A[Int].
g requires no warning because X=A[Int], P=B[Int], XR=B[Int], and B[Int] <:< B[Int].
XR=B[Int] because a value of type A[Int] which is tested to be a B can
only be a B[Int], due to the definition of B (B[T] extends A[T].)
This is something like asSeenFrom, only rather than asking what a type looks like from the point of view of one of its base classes, we ask what it looks like from the point of view of one of its subclasses.
- Self Type
- Analyzer
- Source
- Checkable.scala
- Alphabetic
- By Inheritance
- Checkable
- AnyRef
- Any
- by any2stringadd
- by StringFormat
- by Ensuring
- by ArrowAssoc
- Hide All
- Show All
- Public
- All
Type Members
- trait InferCheckable extends AnyRef
Value Members
-
final
def
!=(arg0: Any): Boolean
- Definition Classes
- AnyRef → Any
-
final
def
##(): Int
- Definition Classes
- AnyRef → Any
- def +(other: String): String
- def ->[B](y: B): (Checkable, B)
-
final
def
==(arg0: Any): Boolean
- Definition Classes
- AnyRef → Any
-
final
def
asInstanceOf[T0]: T0
- Definition Classes
- Any
-
def
clone(): AnyRef
- Attributes
- protected[java.lang]
- Definition Classes
- AnyRef
- Annotations
- @throws( ... )
- def ensuring(cond: (Checkable) ⇒ Boolean, msg: ⇒ Any): Checkable
- def ensuring(cond: (Checkable) ⇒ Boolean): Checkable
- def ensuring(cond: Boolean, msg: ⇒ Any): Checkable
- def ensuring(cond: Boolean): Checkable
-
final
def
eq(arg0: AnyRef): Boolean
- Definition Classes
- AnyRef
-
def
equals(arg0: Any): Boolean
- Definition Classes
- AnyRef → Any
-
def
finalize(): Unit
- Attributes
- protected[java.lang]
- Definition Classes
- AnyRef
- Annotations
- @throws( classOf[java.lang.Throwable] )
- def formatted(fmtstr: String): String
-
final
def
getClass(): Class[_]
- Definition Classes
- AnyRef → Any
-
def
hashCode(): Int
- Definition Classes
- AnyRef → Any
-
final
def
isInstanceOf[T0]: Boolean
- Definition Classes
- Any
-
final
def
ne(arg0: AnyRef): Boolean
- Definition Classes
- AnyRef
-
final
def
notify(): Unit
- Definition Classes
- AnyRef
-
final
def
notifyAll(): Unit
- Definition Classes
- AnyRef
-
def
propagateKnownTypes(from: Global.Type, to: Global.Symbol): Global.Type
The applied type of class 'to' after inferring anything possible from the knowledge that 'to' must also be of the type given in 'from'.
-
final
def
synchronized[T0](arg0: ⇒ T0): T0
- Definition Classes
- AnyRef
-
def
toString(): String
- 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): (Checkable, B)
The Scala compiler and reflection APIs.