Merge pull request #1761 from dotty-staging/topic/product-show

[REPL] Add show capability to common types

2 files changed, 171 insertions, 0 deletions

diff --git a/library/src/dotty/Show.scala b/library/src/dotty/Show.scala
new file mode 100644
index 000000000..2feeb29ef
--- /dev/null
+++ b/library/src/dotty/Show.scala
@@ -0,0 +1,102 @@
+package dotty
+
+import scala.annotation.implicitNotFound
+
+@implicitNotFound("No member of type class Show could be found for ${T}")
+trait Show[-T] {
+  def show(t: T): String
+}
+
+/** Ideally show would only contain `defaultShow` and the pimped generic class,
+  * but since we can't change the current stdlib, we're stuck with providing
+  * default instances in this object
+  */
+object Show {
+  private[this] val defaultShow: Show[Any] = new Show[Any] {
+    def show(x: Any) = x.toString
+  }
+
+  /** This class implements pimping of all types to provide a show method.
+    * Currently it is quite permissive, if there's no instance of `Show[T]` for
+    * any `T`, we default to `T#toString`.
+    */
+  implicit class ShowValue[V](val v: V) extends AnyVal {
+    def show(implicit ev: Show[V] = defaultShow): String =
+      ev.show(v)
+  }
+
+  implicit val stringShow: Show[String] = new Show[String] {
+    // From 2.12 spec, `charEscapeSeq`:
+    // ‘\‘ (‘b‘ | ‘t‘ | ‘n‘ | ‘f‘ | ‘r‘ | ‘"‘ | ‘'‘ | ‘\‘)
+    def show(str: String) =
+      "\"" + {
+        val sb = new StringBuilder
+        str.foreach {
+          case '\b' => sb.append("\\b")
+          case '\t' => sb.append("\\t")
+          case '\n' => sb.append("\\n")
+          case '\f' => sb.append("\\f")
+          case '\r' => sb.append("\\r")
+          case '\'' => sb.append("\\'")
+          case '\"' => sb.append("\\\"")
+          case c => sb.append(c)
+        }
+        sb.toString
+      } + "\""
+  }
+
+  implicit val intShow: Show[Int] = new Show[Int] {
+    def show(i: Int) = i.toString
+  }
+
+  implicit val floatShow: Show[Float] = new Show[Float] {
+    def show(f: Float) = f + "f"
+  }
+
+  implicit val doubleShow: Show[Double] = new Show[Double] {
+    def show(d: Double) = d.toString
+  }
+
+  implicit val charShow: Show[Char] = new Show[Char] {
+    def show(c: Char) = "'" + (c match {
+      case '\b' => "\\b"
+      case '\t' => "\\t"
+      case '\n' => "\\n"
+      case '\f' => "\\f"
+      case '\r' => "\\r"
+      case '\'' => "\\'"
+      case '\"' => "\\\""
+      case c    => c
+    }) + "'"
+  }
+
+  implicit def showList[T](implicit st: Show[T]): Show[List[T]] = new Show[List[T]] {
+    def show(xs: List[T]) =
+      if (xs.isEmpty) "Nil"
+      else "List(" + xs.map(_.show).mkString(", ") + ")"
+  }
+
+  implicit val showNil: Show[Nil.type] = new Show[Nil.type] {
+    def show(xs: Nil.type) = "Nil"
+  }
+
+  implicit def showOption[T](implicit st: Show[T]): Show[Option[T]] = new Show[Option[T]] {
+    def show(ot: Option[T]): String = ot match {
+      case Some(t) => "Some("+ st.show(t) + ")"
+      case none => "None"
+    }
+  }
+
+  implicit val showNone: Show[None.type] = new Show[None.type] {
+    def show(n: None.type) = "None"
+  }
+
+  implicit def showMap[K,V](implicit sk: Show[K], sv: Show[V]): Show[Map[K,V]] = new Show[Map[K,V]] {
+    def show(m: Map[K, V]) =
+      "Map(" + m.map { case (k, v) => sk.show(k) + " -> " + sv.show(v) } .mkString (", ") + ")"
+  }
+
+  implicit def showMapOfNothing: Show[Map[Nothing,Nothing]] = new Show[Map[Nothing,Nothing]] {
+    def show(m: Map[Nothing, Nothing]) = m.toString
+  }
+}
diff --git a/library/test/dotty/ShowTests.scala b/library/test/dotty/ShowTests.scala
new file mode 100644
index 000000000..7230106d5
--- /dev/null
+++ b/library/test/dotty/ShowTests.scala
@@ -0,0 +1,69 @@
+package dotty
+
+import org.junit.Test
+import org.junit.Assert._
+
+class ShowTests {
+  import Show._
+
+  @Test def showString = {
+    assertEquals("\"\\thello world!\"", "\thello world!".show)
+    assertEquals("\"\\nhello world!\"", "\nhello world!".show)
+    assertEquals("\"\\rhello world!\"", "\rhello world!".show)
+    assertEquals("\"\\b\\t\\n\\f\\r\\\'\\\"\"", "\b\t\n\f\r\'\"".show)
+  }
+
+  @Test def showFloat = {
+    assertEquals("1.0f", 1.0f.show)
+    assertEquals("1.0f", 1.0F.show)
+  }
+
+  @Test def showDouble = {
+    assertEquals("1.0", 1.0d.show)
+    assertEquals("1.0", 1.0.show)
+  }
+
+  @Test def showChar = {
+    assertEquals("'\\b'", '\b'.show)
+    assertEquals("'\\t'", '\t'.show)
+    assertEquals("'\\n'", '\n'.show)
+    assertEquals("'\\f'", '\f'.show)
+    assertEquals("'\\r'", '\r'.show)
+    assertEquals("'\\''", '\''.show)
+    assertEquals("'\\\"'", '\"'.show)
+  }
+
+  @Test def showCar = {
+    case class Car(model: String, manufacturer: String, year: Int)
+    implicit val showCar = new Show[Car] {
+      def show(c: Car) =
+        "Car(" + c.model.show + ", " + c.manufacturer.show + ", " + c.year.show + ")"
+    }
+
+    case class Shop(xs: List[Car], name: String)
+    implicit val showShop = new Show[Shop] {
+      def show(sh: Shop) =
+        "Shop(" + sh.xs.show + ", " + sh.name.show + ")"
+    }
+
+    assertEquals("Car(\"Mustang\", \"Ford\", 1967)", Car("Mustang", "Ford", 1967).show)
+  }
+
+  @Test def showOptions = {
+    assertEquals("None", None.show)
+    assertEquals("None", (None: Option[String]).show)
+    assertEquals("Some(\"hello opt\")", Some("hello opt").show)
+  }
+
+  @Test def showMaps = {
+    val mp = scala.collection.immutable.Map("str1" -> "val1", "str2" -> "val2")
+    assertEquals("Map(\"str1\" -> \"val1\", \"str2\" -> \"val2\")", mp.show)
+  }
+
+  @Test def withoutShow = {
+    case class Car(model: String, manufacturer: String, year: Int)
+
+    assertEquals("Car(Mustang,Ford,1967)", Car("Mustang", "Ford", 1967).show)
+    assertEquals("Map()", Map().show)
+  }
+}