Make Prop.label argument by-name.

Author: mrdziuban

core/shared/src/main/scala/org/scalacheck/Prop.scala

@@ -149,19 +149,19 @@ sealed abstract class Prop extends Serializable { self =>
   override def toString = "Prop"
 
   /** Put a label on the property to make test reports clearer */
-  def label(l: String) = map(_.label(l))
+  def label(l: => String) = map(_.label(l))
 
   /** Put a label on the property to make test reports clearer */
-  def :|(l: String) = label(l)
+  def :|(l: => String) = label(l)
 
   /** Put a label on the property to make test reports clearer */
-  def |:(l: String) = label(l)
+  def |:(l: => String) = label(l)
 
   /** Put a label on the property to make test reports clearer */
-  def :|(l: Symbol) = label(l.name)
+  def :|(l: => Symbol)(implicit d: DummyImplicit) = label(l.name)
 
   /** Put a label on the property to make test reports clearer */
-  def |:(l: Symbol) = label(l.name)
+  def |:(l: => Symbol)(implicit d: DummyImplicit) = label(l.name)
 
 }
 
@@ -214,7 +214,10 @@ object Prop {
 
     def collect(x: Any) = copy(collected = collected + x)
 
-    def label(l: String) = copy(labels = labels + (() => l))
+    def label(l: => String) = {
+      lazy val label = l
+      copy(labels = labels + (() => label))
+    }
 
     def &&(r: Result) = (this.status, r.status) match {
       case (Exception(_), _) => this