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/*
 * Copyright 2001-2013 Artima, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.scalatest.enablers

/**
 * Supertrait for typeclasses that enable the exist matcher syntax.
 *
 * 
 * An Existence[S] provides access to the "existence nature" of type S in such
 * a way that exist matcher syntax can be used with type S. A S
 * can be any type for which the concept of existence makes sense, such as java.io.File. ScalaTest provides
 * implicit implementations for java.io.File. You can enable the exist matcher syntax on your own
 * type U by defining a Existence[U] for the type and making it available implicitly.
 * 
 * 

 * ScalaTest provides an implicit Existence instance for java.io.File
 * in the Existence companion object.
 * 
 */
trait Existence[-S] {

  /**
   * Determines whether the passed thing exists, i.e., whether the passed java.io.File exists.
   *
   * @param thing the thing to check for existence
   * @return true if passed thing exists, false otherwise
   */
  def exists(thing: S): Boolean
}

/**
 * Companion object for Existence that provides implicit implementations for java.io.File.
 */
object Existence {

  /**
   * Enable Existence implementation for java.io.File
   *
   * @tparam FILE any subtype of java.io.File
   * @return Existence[FILE] that supports java.io.File in exist syntax
   */
  implicit def existenceOfFile[FILE <: java.io.File]: Existence[FILE] =
    new Existence[FILE] {
      def exists(file: FILE): Boolean = file.exists
    }
  
}