|
[#788] |
project: compiler |
priority: low |
category: bug |
|---|
|
submitter |
assigned to |
status |
date submitted |
|
Sean |
Martin |
fixed |
2006-10-23 23:57:44.0 |
| subject |
match casts combined with original type broken |
| code |
package test;
trait Test {
type Node <: NodeImpl;
trait NodeImpl;
type Expression <: Node with ExpressionImpl;
trait ExpressionImpl extends NodeImpl {
def self : Expression;
}
type Named <: Node with NamedImpl;
trait NamedImpl extends NodeImpl {
def self : Named;
}
def asExpression(e : ExpressionImpl) : Named = {
e match {
case f : NamedImpl => f.self;
case _ => null;
}
}
}
|
| what happened |
ype mismatch;
found : Test.this.Expression
required: Test.this.Named test24/src/test Test.scala line 16 1161637333617 184924
|
| what expected |
f.self should resolve to self call in NamedImpl, not ExpressionImpl. The work around here is to upcast e to any (using (e:Any) match...) to throw off any type combinations by the matcher. To avoid upcasting, the type of the match should occur after types derived from the value being matched. In this example, the type of f is NamedImpl with ExpressionImpl, but should be ExpressionImpl with NamedImpl (I guess....), or better yet: Expression with NamedImpl (why does matching throw off the type parameter?).
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