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    //! impl bool {}

    #[lang = "bool"]
    impl bool {
        /// Returns `Some(t)` if the `bool` is `true`, or `None` otherwise.
        ///
        /// # Examples
        ///
        /// ```
        /// #![feature(bool_to_option)]
        ///
        /// assert_eq!(false.then(0), None);
        /// assert_eq!(true.then(0), Some(0));
        /// ```
        #[unstable(feature = "bool_to_option", issue = "64260")]
        #[inline]
        pub fn then<T>(self, t: T) -> Option<T> {
            if self {
                Some(t)
            } else {
                None
            }
        }

        /// Returns `Some(f())` if the `bool` is `true`, or `None` otherwise.
        ///
        /// # Examples
        ///
        /// ```
        /// #![feature(bool_to_option)]
        ///
        /// assert_eq!(false.then_with(|| 0), None);
        /// assert_eq!(true.then_with(|| 0), Some(0));
        /// ```
        #[unstable(feature = "bool_to_option", issue = "64260")]
        #[inline]
        pub fn then_with<T, F: FnOnce() -> T>(self, f: F) -> Option<T> {
            if self {
                Some(f())
            } else {
                None
            }
        }
    }