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bool.dart
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bool.dart
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// 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;
// Examples can assume:
// class Logger { const Logger({String id}); }
/// The reserved words `true` and `false` denote objects that are the only two
/// instances of this class.
///
/// It is a compile-time error for a class to attempt to extend or implement
/// bool.
@pragma("vm:entry-point")
final class bool {
/// Boolean value for [name] in the compilation configuration environment.
///
/// The compilation configuration environment is provided by the
/// surrounding tools which are compiling or running the Dart program.
/// The environment is a mapping from a set of string keys to their associated
/// string value.
/// The string value, or lack of a value, associated with a [name]
/// must be consistent across all calls to [String.fromEnvironment],
/// [int.fromEnvironment], `bool.fromEnvironment` and [bool.hasEnvironment]
/// in a single program.
/// The string values can be directly accessed using [String.fromEnvironment].
///
/// This constructor parses the string value associated with [name] as
/// a boolean, as if by [`bool.tryParse(value)`][bool.tryParse],
/// meaning that it accepts only the strings `"true"` and `"false"`.
///
/// If there is no value associated with [name] in the compilation
/// configuration environment, or if the associated string value is not one
/// of `"true"` or `"false"`, the value of the constructor invocation
/// is the [defaultValue] boolean, which defaults to the boolean value
/// `false`.
///
/// The result is the same as that of:
/// ```dart template:expression
/// (const String.fromEnvironment(name) == "true")
/// || ((const String.fromEnvironment(name) != "false") && defaultValue)
/// ```
///
/// Example:
/// ```dart
/// const bool loggingEnabled = bool.fromEnvironment("logging");
/// ```
/// In order to check whether a value is there at all, use
/// [bool.hasEnvironment]. Example:
/// ```dart
/// const bool? yesNoMaybe = bool.hasEnvironment("optionalFlag")
/// ? bool.fromEnvironment("optionalFlag")
/// : null;
/// ```
///
/// To accept other strings than `"true"` or `"false"`, use the
/// [String.fromEnvironment] constructor directly. Example:
/// ```dart
/// const isLoggingOn = (const String.fromEnvironment("logging") == "on");
/// ```
///
/// This constructor is only guaranteed to work when invoked as `const`.
/// It may work as a non-constant invocation on some platforms which
/// have access to compiler options at run-time, but most ahead-of-time
/// compiled platforms will not have this information.
external const factory bool.fromEnvironment(String name,
{bool defaultValue = false});
/// Whether [name] is declared in the compilation configuration environment.
///
/// The compilation configuration environment is provided by the
/// surrounding tools which are compiling or running the Dart program.
/// The environment is a mapping from a set of string keys to their associated
/// string value.
/// The string value, or lack of a value, associated with a [name]
/// must be consistent across all calls to [String.fromEnvironment],
/// [int.fromEnvironment], `bool.fromEnvironment` and [bool.hasEnvironment]
/// in a single program.
///
/// This constructor evaluates to `true` if [name] has an associated value
/// in the compilation configuration environment, and to `false` if not.
/// If there is an associated value, then the value can be accessed using
/// `const String.fromEnvironment(name)`. Otherwise,
/// `String.fromEnvironment(name, defaultValue: someString)`
/// is known to evaluate to the given `defaultValue`.
///
/// The [String.fromEnvironment], [int.fromEnvironment] and
/// [bool.fromEnvironment] constructors always produce a [String], [int],
/// or [bool], as required for a constructor.
/// In most cases, the absence of a configuration environment association
/// for a [name] simply means that the code should fall back on a default
/// behavior, and a default value of the same type typically represents that
/// perfectly.
///
/// In some cases, a value of different type, mostly `null`, may better
/// represent the absence of a choice. In that case, this constructor can
/// be used to first check whether there is a value, and only then use the
/// other `fromEnvironment` constructors.
/// Example:
/// ```dart
/// const int? indentOverride = bool.hasEnvironment("indent-override")
/// ? int.fromEnvironment("indent-override")
/// : null;
/// void indentLines(List<String> lines, int indentation) {
/// int actualIndentation = indentOverride ?? indentation;
/// // ... Do something to lines.
/// }
/// ```
/// This pattern allows a compilation configuration to provide an override
/// value to the program, but also to not do so, and the program can tell the
/// difference between an explicitly provided value and the absence of one.
///
/// Another use case is to only do something extra when a needed value is
/// available. Example:
/// ```dart
/// const Logger? logger = bool.hasEnvironment("logging-id")
/// ? Logger(id: String.fromEnvironment("logging-id"))
/// : null;
/// ```
///
/// This constructor is only guaranteed to work when invoked as `const`.
/// It may work as a non-constant invocation on some platforms which
/// have access to compiler options at run-time, but most ahead-of-time
/// compiled platforms will not have this information.
external const factory bool.hasEnvironment(String name);
/// Parses [source] as an, optionally case-insensitive, boolean literal.
///
/// If [caseSensitive] is `true`, which is the default,
/// the only accepted inputs are the strings `"true"` and `"false"`,
/// which returns the results `true` and `false` respectively.
///
/// If [caseSensitive] is `false`, any combination of upper and lower case
/// ASCII letters in the words `"true"` and `"false"` are accepted,
/// as if the input was first lower-cased.
///
/// Throws a [FormatException] if the [source] string does not contain
/// a valid boolean literal.
///
/// Rather than throwing and immediately catching the [FormatException],
/// instead use [tryParse] to handle a potential parsing error.
///
/// Example:
/// ```dart
/// print(bool.parse('true')); // true
/// print(bool.parse('false')); // false
/// print(bool.parse('TRUE')); // throws FormatException
/// print(bool.parse('TRUE', caseSensitive: false)); // true
/// print(bool.parse('FALSE', caseSensitive: false)); // false
/// print(bool.parse('NO')); // throws FormatException
/// print(bool.parse('YES')); // throws FormatException
/// print(bool.parse('0')); // throws FormatException
/// print(bool.parse('1')); // throws FormatException
/// ```
@Since("3.0")
external static bool parse(String source, {bool caseSensitive = true});
/// Parses [source] as an, optionally case-insensitive, boolean literal.
///
/// If [caseSensitive] is `true`, which is the default,
/// the only accepted inputs are the strings `"true"` and `"false"`,
/// which returns the results `true` and `false` respectively.
///
/// If [caseSensitive] is `false`, any combination of upper and lower case
/// ASCII letters in the words `"true"` and `"false"` are accepted,
/// as if the input was first lower-cased.
///
/// Returns `null` if the [source] string does not contain a valid
/// boolean literal.
///
/// If the input can be assumed to be valid, use [bool.parse] to avoid
/// having to deal with a possible `null` result.
///
/// Example:
/// ```dart
/// print(bool.tryParse('true')); // true
/// print(bool.tryParse('false')); // false
/// print(bool.tryParse('TRUE')); // null
/// print(bool.tryParse('TRUE', caseSensitive: false)); // true
/// print(bool.tryParse('FALSE', caseSensitive: false)); // false
/// print(bool.tryParse('NO')); // null
/// print(bool.tryParse('YES')); // null
/// print(bool.tryParse('0')); // null
/// print(bool.tryParse('1')); // null
/// ```
@Since("3.0")
external static bool? tryParse(String source, {bool caseSensitive = true});
external int get hashCode;
/// The logical conjunction ("and") of this and [other].
///
/// Returns `true` if both this and [other] are `true`, and `false` otherwise.
@Since("2.1")
bool operator &(bool other) => other && this;
/// The logical disjunction ("inclusive or") of this and [other].
///
/// Returns `true` if either this or [other] is `true`, and `false` otherwise.
@Since("2.1")
bool operator |(bool other) => other || this;
/// The logical exclusive disjunction ("exclusive or") of this and [other].
///
/// Returns whether this and [other] are neither both `true` nor both `false`.
@Since("2.1")
bool operator ^(bool other) => !other == this;
/// Returns either `"true"` for `true` and `"false"` for `false`.
String toString() {
return this ? "true" : "false";
}
}