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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;
/// 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 {
/// 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].
///
/// The result is the same as would be returned by:
/// ```dart template:expression
/// (const String.fromEnvironment(name) == "true")
/// ? true
/// : (const String.fromEnvironment(name) == "false")
/// ? false
/// : defaultValue
/// ```
/// Example:
/// ```dart
/// const loggingFlag = const bool.fromEnvironment("logging");
/// ```
/// If you want to use a different truth-string than `"true"`, you can use the
/// [String.fromEnvironment] constructor directly:
/// ```dart
/// const isLoggingOn = (const String.fromEnvironment("logging") == "on");
/// ```
///
/// 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 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.
// The .fromEnvironment() constructors are special in that we do not want
// users to call them using "new". We prohibit that by giving them bodies
// that throw, even though const constructors are not allowed to have bodies.
// Disable those static errors.
//ignore: const_constructor_with_body
//ignore: const_factory
external const factory bool.fromEnvironment(String name,
{bool defaultValue = false});
/// Whether there is an environment declaration [name].
///
/// Returns true iff there is an environment declaration with the name [name]
/// If there is then the value of that declaration can be accessed using
/// `const String.fromEnvironment(name)`. Otherwise,
/// `String.fromEnvironment(name, defaultValue: someString)`
/// will evaluate to the given `defaultValue`.
///
/// This constructor can be used to handle an absent declaration
/// specifically, in ways that cannot be represented by providing
/// a default value to the `C.fromEnvironment` constructor where `C`
/// is one of [String], [int], or [bool].
///
/// Example:
/// ```dart
/// const loggingIsDeclared = bool.hasEnvironment("logging");
///
/// const String? logger = loggingIsDeclared
/// ? String.fromEnvironment("logging")
/// : null;
/// ```
///
/// 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 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.
// The .hasEnvironment() constructor is special in that we do not want
// users to call them using "new". We prohibit that by giving them bodies
// that throw, even though const constructors are not allowed to have bodies.
// Disable those static errors.
//ignore: const_constructor_with_body
//ignore: const_factory
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.tryParse('true')); // true
/// print(bool.tryParse('false')); // false
/// print(bool.tryParse('TRUE')); // throws FormatException
/// print(bool.tryParse('TRUE', caseSensitive: false)); // true
/// print(bool.tryParse('FALSE', caseSensitive: false)); // false
/// print(bool.tryParse('NO')); // throws FormatException
/// print(bool.tryParse('YES')); // throws FormatException
/// print(bool.tryParse('0')); // throws FormatException
/// print(bool.tryParse('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";
}
}