问题
I would like to write an annotation macro that adds an extends <sometype> to traits where <sometype> can be specified at compile time.
How can a compile time parameter be passed to a macro expansion? Ideally I would like to specify a command line argument at the compiler call.
回答1:
Macro annotations don't have access to the command-line flags passed to scalac. However, one possible way to achieve this might be to use system properties.
For example, in the macro annotation implementation
// MyMacro.scala
val someType = sys.props.getOrElse("myapp.sometype", ???)
Then pass the type as a command line option
// command-line
scalac -Dmyapp.sometype=foobar Code.scala
Similarly, it's possible to run sbt -Dsometype=foobar compile. However, note that the JVM process needs to start with the system property flag, so setting scalacOptions += "-Dsometype=foobar" may not work.
来源：https://stackoverflow.com/questions/42969692/compile-time-parameter-for-macro-expansion