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Standard library for the Scala Programming Language
There is a newer version: 2.13.13
/*
 * Scala (https://www.scala-lang.org)
 *
 * Copyright EPFL and Lightbend, Inc.
 *
 * Licensed under Apache License 2.0
 * (http://www.apache.org/licenses/LICENSE-2.0).
 *
 * See the NOTICE file distributed with this work for
 * additional information regarding copyright ownership.
 */

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.
 */
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]

  // Do not open until 2.12.
  //** This value if the property is set, an alternative value otherwise. */
  //def or[T1 >: T](alt: => T1): T1

  /** 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
}