Scala macros invoke a compile-time determined function name

Question

I have the following code:

def invokeFunction(logger: Logger, fName: String) = macro invokeFunctionImpl

//...

def invokeFunctionImpl(c: Context)(logger: c.Expr[Logger], fName: c.Expr[String]) ={
  import c.universe._
  // i'd like to invoke: logger.${fName}("some message")
}

Another problem I'm facing is naming a function during compile-time, using a given argument:

def createFunction(fName: String) = macro createFunctionImpl

//...

def createFunctionImpl(c: Context)(fName: c.Expr[String], param: c.Expr[String]) ={
  import c.universe._
  // i'd like to create: def functionNamed${fName}(param: [paramType]) = {
    // implementation unimportant
}

Any help would be appreciated.

Answer 1

invokeFunction should be like

def invokeFunction(logger: Logger, fName: String): Unit = macro invokeFunctionImpl

def invokeFunctionImpl(c: blackbox.Context)(logger: c.Expr[Logger], fName: c.Expr[String]): c.Expr[Unit] ={
  import c.universe._
  val q"${fNameStr: String}" = fName.tree
  c.Expr(q"""$logger.${TermName(fNameStr)}("some message")""")
}

I added return type. I assume that fName is a compile-time String literal (otherwise you'll have MatchError ).

Regarding createFunction try

def createFunction(fName: String, param: String): Unit = macro createFunctionImpl

def createFunctionImpl(c: blackbox.Context)(fName: c.Expr[String], param: c.Expr[String]): c.Expr[Unit] ={
  import c.universe._
  val q"${fNameStr: String}" = fName.tree
  val q"${paramNameStr: String}" = param.tree

  c.Expr(q"""
    def ${TermName(fNameStr)}(${TermName(paramNameStr)}: ParamType) = ???

    ()
  """)
}

Please notice that signatures of macro and its implementation must correspond to each other. So I added param to createFunction . And I added return type. Also it's important that a function being created will be accessible only inside the block that our macro is expanded to. New definitions is not what def macros are normally intended for ( macro annotations are).

I'm not sure I understand completely what you're doing. It will be easier to answer if you provide code how you're going to use your macros.