Scala example source code file (Prop.scala)

This example Scala source code file (Prop.scala) is included in my "Source Code Warehouse" project. The intent of this project is to help you more easily find Scala source code examples by using tags.

All credit for the original source code belongs to scala-lang.org; I'm just trying to make examples easier to find. (For my Scala work, see my Scala examples and tutorials.)

Scala tags/keywords

boolean, creator, creatorimpl, doubleprop, no, prop, string, stringprop, t, unit

The Prop.scala Scala example source code

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2003-2013, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */

package scala
package sys

/** A lightweight interface wrapping a property contained in some
 *  unspecified map.  Generally it'll be the system properties but this
 *  is not a requirement.
 *
 *  See `scala.sys.SystemProperties` for an example usage.
 *
 *  @author Paul Phillips
 *  @version 2.9
 *  @since   2.9
 */
trait Prop[+T] {
  /** The full name of the property, e.g. "java.awt.headless".
   */
  def key: String

  /** If the key exists in the properties map, converts the value
   *  to type `T` using valueFn.  As yet no validation is performed:
   *  it will throw an exception on a failed conversion.
   *  @return   the converted value, or `zero` if not in the map
   */
  def value: T

  /** True if the key exists in the properties map.  Note that this
   *  is not sufficient for a Boolean property to be considered true.
   *  @return   whether the map contains the key
   */
  def isSet: Boolean

  /** Sets the property.
   *
   *  @param    newValue  the new string value
   *  @return   the old value, or null if it was unset.
   */
  def set(newValue: String): String

  /** Sets the property with a value of the represented type.
   */
  def setValue[T1 >: T](value: T1): T

  /** Gets the current string value if any.  Will not return null: use
   *  `isSet` to test for existence.
   *  @return   the current string value if any, else the empty string
   */
  def get: String

  /** Some(value) if the property is set, None otherwise.
   */
  def option: Option[T]

  /** Removes the property from the underlying map.
   */
  def clear(): Unit

  /** A value of type `T` for use when the property is unset.
   *  The default implementation delivers null for reference types
   *  and 0/0.0/false for non-reference types.
   */
  protected def zero: T
}

object Prop {
  /** A creator of property instances.  For any type `T`, if an implicit
   *  parameter of type Creator[T] is in scope, a Prop[T] can be created
   *  via this object's apply method.
   */
  @annotation.implicitNotFound("No implicit property creator available for type ${T}.")
  trait Creator[+T] {
    /** Creates a Prop[T] of this type based on the given key. */
    def apply(key: String): Prop[T]
  }

  implicit object FileProp extends CreatorImpl[java.io.File](s => new java.io.File(s))
  implicit object StringProp extends CreatorImpl[String](s => s)
  implicit object IntProp extends CreatorImpl[Int](_.toInt)
  implicit object DoubleProp extends CreatorImpl[Double](_.toDouble)

  def apply[T: Creator](key: String): Prop[T] = implicitly[Creator[T]] apply key
}