scala-macros

I have the next code, and i would like to extract the default parametr from value. // def extractor[T] = macro extractorImpl[T] def extractorImpl[T: c.WeakTypeTag](c: Context) = { //first i got a type contructor ??? } i try with attachments but attachments.all return a Set[Any] with (for example) SymbolSourceAttachment(val name: String = "new name") SymbolSourceAttachment contain ValDef but i do not know how to extract from SymbolSourceAttachment ValDef . By the way i should to get a Map[String, String]("name" -> "new name") Example: case class Person(name: String = "new name") object Macro {

I have a scala macro which outputs nested case classes. I can assemble fragments of expressions created using reify to build up the nested case classes programmatically: case class Foo(name: String) case class Bar(foo: Foo) def foo(name: String) = { c.universe reify { Foo(c.literal(name).splice) } } def bar(foo: Expr[Foo]) = { c.universe reify { Bar(foo.splice) } } // output Bar(Foo("MyFoo")) c.Expr( bar(foo("MyFoo").asInstanceOf[Expr[Foo]]).tree ) Things work well apart from the annoying cast (how can i fix that?). Where I am stuck is when I want the macro to output some case class which

On my scala code, I want to be able to instantiate a new class. For instance, supose I have the code below: class Foo { def foo=10 } trait Bar { val bar=20 } Ideally, I want to be able to do something like: def newInstance[A <: Foo] = { new A with Bar } newInstance[Foo] But, of course this doesn't work. I tried to use reflection to instantiate a class, but it seems that I'm only able to instantiate a new class (and not mix-in with a trait). I think it would be possible to make this work using Macros, but I'm not sure even where to start. What I'm trying to do is like the following Ruby code:

Consider the default codec as offered in the io package. implicitly[io.Codec].name //res0: String = UTF-8 It's a "low priority" implicit so it's easy to override without ambiguity. implicit val betterCodec: io.Codec = io.Codec("US-ASCII") implicitly[io.Codec].name //res1: String = US-ASCII It's also easy to raise its priority level. import io.Codec.fallbackSystemCodec implicit val betterCodec: io.Codec = io.Codec("US-ASCII") implicitly[io.Codec].name //won't compile: ambiguous implicit values But can we go in the opposite direction? Can we create a low level implicit that disables ("ambiguates

Thanks to the answers to my previous question , I was able to create a function macro such that it returns a Map that maps each field name to its value of a class, e.g. ... trait Model case class User (name: String, age: Int, posts: List[String]) extends Model { val numPosts: Int = posts.length ... def foo = "bar" ... } So this command val myUser = User("Foo", 25, List("Lorem", "Ipsum")) myUser.asMap returns Map("name" -> "Foo", "age" -> 25, "posts" -> List("Lorem", "Ipsum"), "numPosts" -> 2) This is where Tuple s for the Map are generated (see Travis Brown's answer ): ... val pairs =

c.inferImplicitValue infers implicit values in the call site scope. Is it possible to infer implicits using the c.prefix scope? This is not valid code, but expresses what I need: c.prefix.inferImplicitValue I'm currently using a naive implementation for this purpose[1], but it has some limitations like not inferring implicit values from def s and detecting duplicated/ambiguous implicit values. [1] https://github.com/getquill/quill/blob/9a28d4e6c901d3fa07e7d5838e2f4c1f3c16732b/quill-core/src/main/scala/io/getquill/util/InferImplicitValueWithFallback.scala#L12 Simply generating a block with an

I'm experimenting with the scala 2.10 macro features. I have trouble using LabelDef in some cases, though. To some extent I peeked in the compiler's code, read excerpts of Miguel Garcia's papers but I'm still stuck. If my understanding is correct , a pseudo-definition would be: LabelDef(labelName, listOfParameters, stmsAndApply) where the 3 arguments are Trees and: - labelName is the identifier of the label $L being defined - listOfParameters correspond to the arguments passed when label- apply occurs, as in $L(a1,...,an) , and can be empty - stmsAndApply corresponds to the block of statements

Update: I suspect that what I want might not be possible, and I've written up a blog post with my reasoning (and some alternatives) here . I'd be very happy to be told that I'm wrong. Suppose I want to create a instance of a trait using a factory method with a macro implementation. This method will take as an argument a path to a resource that the macro will read and parse (at compile time) into a map from strings to strings. That part is all fairly straightforward. Now suppose I want to associate the resulting map with the instance I'm creating so that I can use it in subsequent macro calls