With a type like trait A[T], finding an implicit in scope is simply implicitly[A[SomeType]]
Can this be done and, if so, how is this done where the type-parameter is replaced with an abstract type member, like in trait A { type T }?
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megri
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You can do
implicitly[A { type T = Int }
but you risk to lose precision:
scala> trait Foo { type T ; val t: T }
defined trait Foo
scala> implicit val intFoo: Foo { type T = Int } = new Foo { type T = Int ; val t = 23 }
intFoo: Foo{type T = Int} = $anon$1@6067b682
scala> implicitly[Foo].t // implicitly loses precision
res0: Foo#T = 23
To solve this problem, you can use the newly introduced the method, from the shapeless library (from which I've take the example above)
scala> the[Foo].t // the retains it
res1: Int = 23
scala> the[Foo].t+13
res2: Int = 36
Gabriele Petronella
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`the` is great, but `implicitly[Foo { type T = Int }]` accomplishes the same thing, and is more directly parallel to the type parameter case. – Travis Brown Aug 21 '14 at 01:21
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right, this is probably and overekill, but I jusy wanted to point out the risk and suggest an alternative :) – Gabriele Petronella Aug 21 '14 at 08:17