In Scala 2.9.1, this does not compile, failing with not found: value b:
case class CaseClass(field: String)
object SomeObject {
//val kludge = field
def x(input: (CaseClass, String) => CaseClass): Unit = ()
val field = x((a, b) => a.copy(field = b))
}
However, this does:
case class CaseClass(field: String)
object SomeObject {
val kludge = field
def x(input: (CaseClass, String) => CaseClass): Unit = ()
val field = x((a, b) => a.copy(field = b))
}
The only difference is the commented line. If this isn't a bug, why is this the intended behavior?
Related
I am just trying things out in scala and I wrote this code
object Main:
def main(args: Array[String]): Unit =
val dInt: Data[Int] = IntData(1)
val dString: Data[String] = StringData("hello")
val Data(deconstructedInt) = dInt // unapply
val Data(deconstructedString) = dString // unapply
println(deconstructedInt)
println(deconstructedString)
sealed trait Data[+T]:
def get: T
case class IntData(get: Int) extends Data[Int]
case class StringData(get: String) extends Data[String]
object Data:
def apply[T](input: T): Data[T] = input match {
case i: Int => IntData(i) //compile error here
case s: String => StringData(s) //compile error here
}
def unapply[T](d: Data[T]): Option[String] = d match {
case IntData(get) => Some(s"int data => get = $get")
case StringData(get) => Some(s"string data => get = $get")
}
I get at the location commented in the code this error
Found: IntData
Required: Data[T]
case i: Int => IntData(i)
why I am getting this error, isn't IntData (or StringData) a subclass of Data ?
IntData is a subtype of Data[Int]. So if T is not Int, IntData is not a subtype of Data[T]. Now, you might say, if input matches the first case, then clearly T is Int. But the compiler is not smart to realise this!
You could try using Scala 3's new match types:
type DataOf[T] = T match {
case Int => IntData
case String => StringData
}
def apply[T](input: T): DataOf[T] = input match {
case i: Int => IntData(i)
case s: String => StringData(s)
}
Another alternative is union types:
def apply(input: Int | String): Data[Int | String] = input match {
case i: Int => IntData(i)
case s: String => StringData(s)
}
However, you will lose type information in doing this. Using the match types solution, apply(42) is inferred to have type IntData. Using the union types solution, it is inferred to have type Data[Int | String].
This way compiler connects the dots between Ts and it works:
object Main:
def main(args: Array[String]): Unit =
val dInt: Data[Int] = IntData(1)
val dString: Data[String] = StringData("hello")
val Data(deconstructedInt) = dInt // unapply
val Data(deconstructedString) = dString // unapply
println(deconstructedInt)
println(deconstructedString)
sealed trait Data[+T]:
def get: T
case class IntData[T <: Int](get: T) extends Data[T]
case class StringData[T <: String](get: T) extends Data[T]
object Data:
def apply[T](input: T): Data[T] = input match {
case i: Int => IntData(i)
case s: String => StringData(s)
}
def unapply[T](d: Data[T]): Option[String] = d match {
case IntData(get) => Some(s"int data => get = $get")
case StringData(get) => Some(s"string data => get = $get")
}
I'm puzzled by the compile error for the line that defines endState. Here is the code:
import java.util.UUID
object Evaluation {
def default: Evaluation[Unit, Unit] = new Evaluation[Unit, Unit](identity)
}
case class Evaluation[From, +To](evaluate: (From) => To)
object FSMLike {
val uuidEmpty: UUID = new UUID(0L, 0L)
val endState: Evaluation[Unit, FSMLike[Nothing]] = new Evaluation(() => FSMEmpty)
lazy val stop: FSMEntry[Unit, Unit, Nothing] = FSMEntry(uuidEmpty, Evaluation.default, endState)
def apply[From1, From2, To](
action: Evaluation[From1, Unit],
nextState: Evaluation[From2, FSMLike[To]]
): (UUID, FSMLike[To]) = {
val uuid = UUID.randomUUID
uuid -> FSMEntry(uuid, action, nextState)
}
}
sealed trait FSMLike[+A]
case object FSMEmpty extends FSMLike[Nothing]
case class FSMEntry[From1, From2, +To](
id: UUID,
action: Evaluation[From1, Unit],
nextState: Evaluation[From2, FSMLike[To]]
) extends FSMLike[To] {
def transition(arg1: From1, arg2: From2): FSMLike[To] = {
action.evaluate(arg1)
nextState.evaluate(arg2)
}
override def toString: String = s"^$id^"
}
Here is the error:
Error:(14, 72) type mismatch;
found : () => FSMEmpty.type (with underlying type () => FSMEmpty.type)
required: Unit => FSMLike[Nothing]
val endState: Evaluation[Unit, FSMLike[Nothing]] = new Evaluation(() => FSMEmpty)
You are trying to pass () => FSMEmpty, a function with no arguments, where a function with one argument of type Unit is expected. Sure, when you use () as an expression, it's the only value of type Unit, but the left-hand side of => isn't an expression.
You should write _ => FSMEmpty instead. { case () => FSMEmpty } would work as well, I think, but there isn't much point to using it.
Edit: I've fixed the problem - I was incorrectly calling .map(f => f.typeSignature.asInstanceOf[TypeRef].args.head) on recursiveOpt, which meant that field.name was giving me the wrong field name in my copy method. I've removed the map and everything is working now.
I am writing a macro that will create a map of update methods for a case class, e.g.
case class Inner(innerStr: String)
case class Outer(outerStr: String, inner: Inner, innerOpt: Option[Inner])
should produce an update map for Outer that is something like
val innerMap = Map("innerStr" -> {(json: JsValue) => Try{(inner: Inner) => inner.copy(innerStr = json)}})
val outerMap = Map("outerStr" -> {(json: JsValue) => Try{(outer: Outer) => outer.copy(outerStr = json)}},
"inner.innerStr" -> {(json: JsValue) => Try{(outer: Outer) => innerMap.get("innerStr").get(json).flatMap(update => outer.copy(inner = update(outer.inner)))},
"innerOpt.innerStr" -> {(json: JsValue) => Try{(outer: Outer) => innerMap.get("innerStr").get(json).flatMap(update => outer.copy(inner = outer.inner.map(inner => update(inner))))})
which would then be called like
val oldOuter = Outer("str", Inner("str"), Some(Inner("str")))
val updatedOuter = outerMap.get("inner.innerStr").get(JsString("newStr")).get(oldOuter)
The idea is that given a json kv pair, I can retrieve the appropriate update method from the map using the key and then apply the update using the value, using implicit conversions to convert from the json value to the appropriate type.
My macro is working for the case of a flat case class, e.g. Inner(innerStr: String), and for a nested case class, e.g. Outer(outerStr: String, inner: Inner). However, the case of the nested option case class, Outer(outerStr: String, innerOpt: Option[Inner]), is crashing the compiler. I'm not sure if I'm doing something disastrously wrong, or if there's a bug in the compiler, or third option. This was done using the Scala 2.11.0-M7 REPL
Below is my code - I'm constructing a Map that accepts String input instead of JsValue input so that I don't need to import the play framework into my REPL. The blacklist filters out fields that should not be in the update map (e.g. one of the case classes we're applying this to has fields like "crypted_password" and "salt" that should never be updated via json sent in through a REST route). baseMethods constructs the key -> method tuples for the flat case, recursiveMethods constructs the key-method tuples for the nested case, and recursiveOptMethods constructs the key-value tuples for the nested option case; at the bottom of the macro these are all merged into a flat sequence and a placed in a Map.
I've tested the code in the recursiveOptMethods quasiquotes to ensure that I'm constructing a properly typed sequence of tuples and haven't found an error (also, this code is extremely similar to the recursiveMethods quasiquotes, which are functioning correctly), and I've tested the code that constructs the base, recursive, and recursiveOpt sequences of symbols and they seem to be doing their job.
Any help as to why I'm crashing the compiler would be greatly appreciated.
import scala.language.experimental.macros
def copyTestImpl[T: c.WeakTypeTag](c: scala.reflect.macros.Context)(blacklist: c.Expr[String]*): c.Expr[Map[String, (String) => scala.util.Try[(T) => T]]] = {
import c.universe._
val blacklistList: Seq[String] = blacklist.map(e => c.eval(c.Expr[String](c.resetAllAttrs(e.tree))))
def isCaseClass(tpe: Type): Boolean = tpe.typeSymbol.isClass && tpe.typeSymbol.asClass.isCaseClass
def isCaseClassOpt(tpe: Type): Boolean = tpe.typeSymbol.name.decoded == "Option" && isCaseClass(tpe.asInstanceOf[TypeRef].args.head)
def rec(tpe: Type): c.Expr[Map[String, (String) => scala.util.Try[(T) => T]]] = {
val typeName = tpe.typeSymbol.name.decoded
val fields = tpe.declarations.collectFirst {
case m: MethodSymbol if m.isPrimaryConstructor => m
}.get.paramss.head.filterNot(field => blacklistList.contains(typeName + "." + field.name.decoded))
val recursive = fields.filter(f => isCaseClass(f.typeSignature))
val recursiveOpt = fields.filter(f => isCaseClassOpt(f.typeSignature))
val base = fields.filterNot(f => isCaseClass(f.typeSignature) || isCaseClassOpt(f.typeSignature))
val recursiveMethods = recursive.map {
field => {
val fieldName = field.name
val fieldNameDecoded = fieldName.decoded
val map = rec(field.typeSignature)
q"""{
val innerMap = $map
innerMap.toSeq.map(tuple => ($fieldNameDecoded + "." + tuple._1) -> {
(str: String) => {
val innerUpdate = tuple._2(str)
innerUpdate.map(innerUpdate => (outer: $tpe) => outer.copy($fieldName = innerUpdate(outer.$fieldName)))
}
})}"""
}}
val recursiveOptMethods = recursiveOpt.map {
field => {
val fieldName = field.name
val fieldNameDecoded = fieldName.decoded
val map = rec(field.typeSignature.asInstanceOf[TypeRef].args.head)
q"""{
val innerMap = $map
innerMap.toSeq.map(tuple => ($fieldNameDecoded + "." + tuple._1) -> {
(str: String) => {
val innerUpdate = tuple._2(str)
innerUpdate.map(innerUpdate => (outer: $tpe) => outer.copy($fieldName = (outer.$fieldName).map(inner => innerUpdate(inner))))
}
})}"""
}}
val baseMethods = base.map {
field => {
val fieldName = field.name
val fieldNameDecoded = fieldName.decoded
val fieldType = field.typeSignature
val fieldTypeName = fieldType.toString
q"""{
$fieldNameDecoded -> {
(str: String) => scala.util.Try {
val x: $fieldType = str
(t: $tpe) => t.copy($fieldName = x)
}.recoverWith {
case e: Exception => scala.util.Failure(new IllegalArgumentException("Failed to parse " + str + " as " + $typeName + "." + $fieldNameDecoded + ": " + $fieldTypeName))
}
}}"""
}}
c.Expr[Map[String, (String) => scala.util.Try[(T) => T]]] {
q"""{ Map((List(..$recursiveMethods).flatten ++ List(..$recursiveOptMethods).flatten ++ List(..$baseMethods)):_*) }"""
}
}
rec(weakTypeOf[T])
}
def copyTest[T](blacklist: String*) = macro copyTestImpl[T]
And the top and bottom of my error from the 2.11.0-M7 REPL when calling copyTest[Outer]() (where Outer has an Option[Inner] field)
scala> copyTest[Outer]()
scala.MatchError: AnyRef
with Product
with Serializable {
val innerStr: String
private[this] val innerStr: String
def <init>(innerStr: String): Inner
def copy(innerStr: String): Inner
def copy$default$1: String #scala.annotation.unchecked.uncheckedVariance
override def productPrefix: String
def productArity: Int
def productElement(x$1: Int): Any
override def productIterator: Iterator[Any]
def canEqual(x$1: Any): Boolean
override def hashCode(): Int
override def toString(): String
override def equals(x$1: Any): Boolean
} (of class scala.reflect.internal.Types$ClassInfoType)
at scala.reflect.internal.Variances$class.inType$1(Variances.scala:181)
at scala.reflect.internal.Variances$$anonfun$inArgs$1$1.apply(Variances.scala:176)
at scala.reflect.internal.Variances$$anonfun$inArgs$1$1.apply(Variances.scala:176)
at scala.reflect.internal.util.Collections$class.map2(Collections.scala:55)
at scala.reflect.internal.SymbolTable.map2(SymbolTable.scala:14)
at scala.reflect.internal.Variances$class.inArgs$1(Variances.scala:176)
at scala.reflect.internal.Variances$class.inType$1(Variances.scala:189)
at scala.reflect.internal.Variances$$anonfun$inArgs$1$1.apply(Variances.scala:176)
at scala.reflect.internal.Variances$$anonfun$inArgs$1$1.apply(Variances.scala:176)
at scala.reflect.internal.util.Collections$class.map2(Collections.scala:55)
at scala.reflect.internal.SymbolTable.map2(SymbolTable.scala:14)
at scala.tools.nsc.typechecker.Analyzer$typerFactory$$anon$3.run(Analyzer.scala:93)
at scala.tools.nsc.Global$Run.compileUnitsInternal(Global.scala:1603)
at scala.tools.nsc.Global$Run.compileUnits(Global.scala:1588)
at scala.tools.nsc.Global$Run.compileSources(Global.scala:1583)
at scala.tools.nsc.interpreter.IMain.compileSourcesKeepingRun(IMain.scala:387)
at scala.tools.nsc.interpreter.IMain$ReadEvalPrint.compileAndSaveRun(IMain.scala:816)
at scala.tools.nsc.interpreter.IMain$ReadEvalPrint.compile(IMain.scala:775)
at scala.tools.nsc.interpreter.IMain$Request.compile$lzycompute(IMain.scala:951)
at scala.tools.nsc.interpreter.IMain$Request.compile(IMain.scala:946)
at scala.tools.nsc.interpreter.IMain.compile(IMain.scala:530)
at scala.tools.nsc.interpreter.IMain.interpret(IMain.scala:518)
at scala.tools.nsc.interpreter.IMain.interpret(IMain.scala:516)
at scala.tools.nsc.interpreter.ILoop.reallyInterpret$1(ILoop.scala:748)
at scala.tools.nsc.interpreter.ILoop.interpretStartingWith(ILoop.scala:793)
at scala.tools.nsc.interpreter.ILoop.command(ILoop.scala:660)
at scala.tools.nsc.interpreter.ILoop.processLine(ILoop.scala:427)
at scala.tools.nsc.interpreter.ILoop.loop(ILoop.scala:444)
at scala.tools.nsc.interpreter.ILoop$$anonfun$process$1.apply$mcZ$sp(ILoop.scala:862)
at scala.tools.nsc.interpreter.ILoop$$anonfun$process$1.apply(ILoop.scala:848)
at scala.tools.nsc.interpreter.ILoop$$anonfun$process$1.apply(ILoop.scala:848)
at scala.reflect.internal.util.ScalaClassLoader$.savingContextLoader(ScalaClassLoader.scala:95)
at scala.tools.nsc.interpreter.ILoop.process(ILoop.scala:848)
at scala.tools.nsc.MainGenericRunner.runTarget$1(MainGenericRunner.scala:81)
at scala.tools.nsc.MainGenericRunner.process(MainGenericRunner.scala:94)
at scala.tools.nsc.MainGenericRunner$.main(MainGenericRunner.scala:103)
at scala.tools.nsc.MainGenericRunner.main(MainGenericRunner.scala)
That entry seems to have slain the compiler. Shall I replay
your session? I can re-run each line except the last one.
I found the problem - originally I had val recursiveOpt = fields.filter(f => isCaseClassOpt(f.typeSignature)).map(f => f.typeSignature.asInstanceOf[TypeRef].args.head), which meant that when I called field.name on the recursiveOpt fields I was getting the wrong name back.
I'm building a web-application using Play and Slick, and find myself in a situation where the user-facing forms are similar, but not exactly the same as the database model.
Hence I have two very similar case classes, and need to map from one to another (e.g. while filling the form for rendering an "update" view).
In the case I'm interested in, the database model case class is a super-set of the form case-class, i.e. the only difference between both is that the database model has two more fields (two identifiers, basically).
What I'm now wondering about is whether there'd be a way to build a small library (e.g. macro-driven) to automatically populate the form case class from the database case class based on the member names. I've seen that it may be possible to access this kind of information via reflection using Paranamer, but I'd rather not venture into this.
Here is a solution using Dynamic because I wanted to try it out. A macro would decide statically whether to emit an apply of a source value method, the default value method, or just to supply a literal. The syntax could look something like newFrom[C](k). (Update: see below for the macro.)
import scala.language.dynamics
trait Invocable extends Dynamic {
import scala.reflect.runtime.currentMirror
import scala.reflect.runtime.universe._
def applyDynamic(method: String)(source: Any) = {
require(method endsWith "From")
def caseMethod(s: Symbol) = s.asTerm.isCaseAccessor && s.asTerm.isMethod
val sm = currentMirror reflect source
val ms = sm.symbol.asClass.typeSignature.members filter caseMethod map (_.asMethod)
val values = ms map (m => (m.name, (sm reflectMethod m)()))
val im = currentMirror reflect this
invokeWith(im, method dropRight 4, values.toMap)
}
def invokeWith(im: InstanceMirror, name: String, values: Map[Name, Any]): Any = {
val at = TermName(name)
val ts = im.symbol.typeSignature
val method = (ts member at).asMethod
// supplied value or defarg or default val for type of p
def valueFor(p: Symbol, i: Int): Any = {
if (values contains p.name) values(p.name)
else ts member TermName(s"$name$$default$$${i+1}") match {
case NoSymbol =>
if (p.typeSignature.typeSymbol.asClass.isPrimitive) {
if (p.typeSignature <:< typeOf[Int]) 0
else if (p.typeSignature <:< typeOf[Double]) 0.0
else ???
} else null
case defarg => (im reflectMethod defarg.asMethod)()
}
}
val args = (for (ps <- method.paramss; p <- ps) yield p).zipWithIndex map (p => valueFor(p._1,p._2))
(im reflectMethod method)(args: _*)
}
}
case class C(a: String, b: Int, c: Double = 2.0, d: Double)
case class K(b: Int, e: String, a: String)
object C extends Invocable
object Test extends App {
val res = C applyFrom K(8, "oh", "kay")
Console println res // C(kay,8,2.0,0.0)
}
Update: Here is the macro version, more for fun than for profit:
import scala.language.experimental.macros
import scala.reflect.macros._
import scala.collection.mutable.ListBuffer
def newFrom[A, B](source: A): B = macro newFrom_[A, B]
def newFrom_[A: c.WeakTypeTag, B: c.WeakTypeTag](c: Context)(source: c.Expr[A]): c.Expr[B] = {
import c.{ literal, literalNull }
import c.universe._
import treeBuild._
import nme.{ CONSTRUCTOR => Ctor }
def caseMethod(s: Symbol) = s.asTerm.isCaseAccessor && s.asTerm.isMethod
def defaulter(name: Name, i: Int): String = s"${name.encoded}$$default$$${i+1}"
val noargs = List[c.Tree]()
// side effects: first evaluate the arg
val side = ListBuffer[c.Tree]()
val src = TermName(c freshName "src$")
side += ValDef(Modifiers(), src, TypeTree(source.tree.tpe), source.tree)
// take the arg as instance of a case class and use the case members
val a = implicitly[c.WeakTypeTag[A]].tpe
val srcs = (a.members filter caseMethod map (m => (m.name, m.asMethod))).toMap
// construct the target, using src fields, defaults (from the companion), or zero
val b = implicitly[c.WeakTypeTag[B]].tpe
val bm = b.typeSymbol.asClass.companionSymbol.asModule
val bc = bm.moduleClass.asClass.typeSignature
val ps = (b declaration Ctor).asMethod.paramss.flatten.zipWithIndex
val args: List[c.Tree] = ps map { case (p, i) =>
if (srcs contains p.name)
Select(Ident(src), p.name)
else bc member TermName(defaulter(Ctor, i)) match {
case NoSymbol =>
if (p.typeSignature.typeSymbol.asClass.isPrimitive) {
if (p.typeSignature <:< typeOf[Int]) literal(0).tree
else if (p.typeSignature <:< typeOf[Double]) literal(0.0).tree
else ???
} else literalNull.tree
case defarg => Select(mkAttributedRef(bm), defarg.name)
}
}
c.Expr(Block(side.toList, Apply(Select(New(mkAttributedIdent(b.typeSymbol)), Ctor), args)))
}
With usage:
case class C(a: String, b: Int, c: Double = 2.0, d: Double)
case class K(b: Int, e: String, a: String) { def i() = b }
val res = newFrom[K, C](K(8, "oh", "kay"))
With Scala's pattern matching I would like to confirm not only that two Strings are equal but for example, whether a String starts with, ends, or is contained in another etc.
I experimented with case classes and extractor objects, neither giving me a concise solution. So the solution I came up with looks like the following:
class StrMatches(private val str: Option[String]) {
def ^(prefix: String) = str.exists(_.startsWith(prefix))
def §(suffix: String) = str.exists(_.endsWith(suffix))
def %(infix: String) = str.exists(_.contains(infix))
def ~(approx: String) = str.exists(_.equalsIgnoreCase(approx))
def /(regex: scala.util.matching.Regex) = str.collect({ case regex() => true }).isDefined
def °(len: Int) = str.exists(_.length == len)
def °°(len: (Int, Int)) = str.exists(a => a.length >= len._1 && a.length <= len._2)
def `\\s*` = str.exists(_.trim.isEmpty)
override def toString = str.mkString
}
object StrMatches {
implicit def apply(x: Str) = new StrMatches(x)
def unapply(x: StrMatches) = x.str
implicit def unwrap(x: StrMatches) = x.toString
}
A client using the StrMatches class could look like the following:
object TestApp extends App {
val str = "foobar"
val strMatches = StrMatches(str)
if (strMatches ^ "foo") {
println(strMatches)
}
if (strMatches § "bar") {
println(strMatches)
}
if (strMatches % "ob") {
println(strMatches)
}
}
As opposed to writing:
object TestApp extends App {
val str: String = null // Just as an illustration for Scala interfacing Java.
if (str != null) {
if (str.startsWith("foo")) {
println(str)
}
if (strMatches.endsWith("bar")) {
println(str)
}
if (strMatches.contains("ob")) {
println(strMatches)
}
}
}
With what kind of solutions would you come up with?
You could use regular expressions. Then you could use pattern matching (which I think was the original intent of your question):
object TestApp extends App {
val str = "foobar"
val StartsWithFooRE = """^foo.*""".r
val EndsWithBarRE = """.*bar$""".r
val ContainsBoRE = """.*bo.*""".r
str match {
case StartsWithFooRE() => println(str)
case EndsWithBarRE() => println(str)
case ContainsBoRE() => println(str)
case _ =>
}
}
To make this more convenient, you could define an object with factory methods to construct the regular expressions. However, due to how pattern matching works, you'll still have to define the expressions outside of the match:
import scala.util.matching.Regex
object RegexFactory {
def startsWith(str: String) = new Regex("^%s.*" format str)
def endsWith(str: String) = new Regex(".*%s$" format str)
def contains(str: String) = new Regex(".*%s.*" format str)
}
object TestApp extends App {
val str = "foobar"
import RegexFactory._
val StartsWithFooRE = startsWith("foo")
val EndsWithBarRE = endsWith("bar")
val ContainsBoRE = contains("bo")
str match {
case StartsWithFooRE() => println(str)
case EndsWithBarRE() => println(str)
case ContainsBoRE() => println(str)
case _ =>
}
}