Re: Factors that prevent implicit conversions to be found

Could it be a case of an implicit with a missing result type?

 - Martin

On Thu, May 21, 2015 at 4:57 PM, Johannes Rudolph
<[email protected]> wrote:
> Hi,
>
> in the akka-http/spray routing DSL there's a case where an implicit
> conversion isn't found in some cases (mostly deterministic per compile
> run) for this line:
>
> parameter('color)
>
> where parameter's argument should be of type `ParamMagnet` and the
> implicit conversion is defined in ParamMagnet's companion object.
>
> There's quite some logic involved behind the scenes to convert a
> Symbol to a ParamMagnet implicit. The strange thing is that you can
> make it compile by adding a line just mentioning the type
> `ParamMagnet` above the problematic line:
>
> e.g.
>
> type X = akka.http.scaladsl.server.directives.ParameterDirectives.ParamMagnet
> parameter('color)
>
> or
>
> val x: akka.http.scaladsl.server.directives.ParameterDirectives.ParamMagnet
> = null
> parameter('color)
>
>
> Adding the line below the problematic one doesn't help. I know it's
> not the first time I had such an issue but I cannot remember if I
> found a solution or not before.
>
> `-Xlog-implicits` doesn't show anything. The compilation problem
> occurs with Scala 2.10.x.
>
> Any ideas?
>
> Thanks,
> Johannes
>
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-- 
Martin Odersky
EPFL

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