content: // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
  // for details. All rights reserved. Use of this source code is governed by a
  // BSD-style license that can be found in the LICENSE file.
  
  part of dart.core;
  
  /**
   * The reserved words [:true:] and [:false:] denote objects that are the only
   * instances of this class.
   *
   * It is a compile-time error for a class to attempt to extend or implement
   * bool.
   */
  class bool {
    /**
     * Returns the boolean value of the environment declaration [name].
     *
     * The boolean value of the declaration is `true` if the declared value is
     * the string `"true"`, and `false` if the value is `"false"`.
     *
     * In all other cases, including when there is no declaration for `name`,
     * the result is the [defaultValue].
     *
     * Example:
     *
     *     const loggingFlag = const bool.fromEnvironment("logging");
     *
     * If you want to use a different truth-string, you can use the
     * [String.fromEnvironment] constructor directly:
     *
     *     const isLoggingOn = (const String.fromEnvironment("logging") == "on");
     */
    external const factory bool.fromEnvironment(String name,
                                                {bool defaultValue: false});
  
    /**
     * Returns [:"true":] if the receiver is [:true:], or [:"false":] if the
     * receiver is [:false:].
     */
    String toString() {
      return this ? "true" : "false";
    }
  }
  