Converted a Scala 2 example from a script to a program

src/main/scala-2/progscala3/metaprogramming/MatchTypeTags.scala

@@ -0,0 +1,77 @@
+// src/main/scala-2/progscala3/metaprogramming/MatchTypeTags.scala
+
+package progscala3.metaprogramming
+
+import scala.reflect.runtime.universe._
+
+/**
+ * This example uses TypeTags, which don't exist in Scala 3.
+ */
+object MatchTypeTags {
+
+  def toType2[T](t: T)(implicit tag: TypeTag[T]): Type = tag.tpe
+  def toType[T : TypeTag](t: T): Type = typeOf[T]
+
+  /**
+   * Return a tuple of the type "prefix", the type's symbol and its
+   * possibly empty list of type parameters.
+   */
+  def toTypeRefInfo[T : TypeTag](x: T): (Type, Symbol, Seq[Type]) = {
+    val TypeRef(pre, typName, parems) = toType(x)
+    (pre, typName, parems)
+  }
+
+  def main(args: Array[String]): Unit = {
+    println(toType(1))
+    println(toType(true))
+    println(toType(Seq(1, true, 3.14)))
+    println(toType((i: Int) => i.toString))
+
+    println(toType2(1))
+    println(toType2(true))
+    println(toType2(Seq(1, true, 3.14)))
+    println(toType2((i: Int) => i.toString))
+
+    assert(toType(1) <:< typeOf[AnyVal] == true)
+    assert(toType(1) <:< toType(1)      == true)
+    assert(toType(1) <:< toType(true)   == false)
+
+    assert(toType(1) =:= typeOf[AnyVal] == false)
+    assert(toType(1) =:= toType(1)      == true)
+    assert(toType(1) =:= toType(true)   == false)
+
+    // (scala.type, class Int, List()):
+    println(toTypeRefInfo(1))
+
+    // (scala.type, class Boolean, List()):
+    println(toTypeRefInfo(true))
+
+    // (scala.collection.type, trait Seq, List(AnyVal)):
+    println(toTypeRefInfo(Seq(1, true, 3.14)))
+
+    // (scala.type, trait Function1, List(Int, java.lang.String)):
+    println(toTypeRefInfo((i: Int) => i.toString))
+
+    val t1 = toType(1)
+    val ts = toType(Seq(1, true, 3.14))
+    val tf = toType((i: Int) => i.toString)
+
+    // Use the reflect.api.types$TypeApi. (The output is long!)
+    def p(msg: String, t: Type): Unit = {
+      println(s"""
+        |For input $msg:
+        |  t.typeSymbol:  ${t.typeSymbol}
+        |  t.erasure:     ${t.erasure}
+        |  t.typeArgs:    ${t.typeArgs}
+        |  t.typeParams:  ${t.typeParams}
+        |  t.companion:   ${t.companion}
+        |  t.decls:       ${t.decls}
+        |  t.members:     ${t.members}
+        |""".stripMargin)
+    }
+
+    p("1:Int", t1)
+    p("Seq(1, true, 3.14)", ts)
+    p("i:Int => String", tf)
+  }
+}