Scala implicit parameters are marked as unused by the compiler

Question

In scala when compiling with -Ywarn-unused, implicit parameters are marked as never used even if they are used in implicit scope.

For example

class MyClass(implicit: ec: ExecutionContext) { def fun = Future.successful("hi").map(_.length) }

This is problematic when running with -Xfatal-warnings as well.

Is there a way to hint to the compiler that these parameters are in fact used? If not, is there another way to ensure code won't compile with unused parameters and declarations?

Not every method from Future need ExecutionContext. Try replacing successful with Future.apply. — Krzysztof Atłasik
– Krzysztof Atłasik, Commented May 29, 2019 at 5:24
@LuisMiguelMejíaSuárez perfect, that's exactly what I was looking for. Go ahead and submit that as an answer! — kag0
– kag0, Commented May 29, 2019 at 18:55

Luis Miguel Mejía Suárez · Accepted Answer · 2019-05-29 19:13:52Z

Use the -Ywarn-macros:after flag too. It basically tells the compiler to make the unused checks after macro expansion, that usually solve the problem of unused implicits.

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