Let's consider the following function:
def printPfType[T](pf:PartialFunction[T, _])(implicit m:Manifest[T]) = {
println(m.toString)
}
Then I define the following test class:
case class Test(s:String, i:Int)
I can't write this:
printPfType {
case Test(_,i) => i
}
because the compiler can't infer the first parametric type of the PartialFunction. 开发者_JS百科I have to specify it explicitly:
printPfType[Test] {
case Test(_,i) => i
}
But then the Test
type appears twice. Is there a technique to avoid this? How can I help the type inferer to avoid the duplicate?
See this thread. Type inference cannot handle this problem. Quote from the spec:
An anonymous function can be defined by a sequence of cases { case p1 => b1 . . . case pn => bn } which appear as an expression without a prior match. The expected type of such an expression must in part be defined. It must be either scala.Functionk[S1, . . . , Sk, R] for some k > 0, or scala.PartialFunction[S1, R], where the argument type(s) S1, . . . , Sk must be fully determined, but the result type R may be undetermined.
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