control_flow.rs - source
Description: Source of the Rust file `library/core/src/ops/control_flow.rs`.
Keywords: rust, rustlang, rust-lang

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    use crate::ops::Try;

    /// Used to make try_fold closures more like normal loops
    #[unstable(feature = "control_flow_enum", reason = "new API", issue = "75744")]
    #[derive(Debug, Clone, Copy, PartialEq)]
    pub enum ControlFlow<B, C = ()> {
        /// Continue in the loop, using the given value for the next iteration
        Continue(C),
        /// Exit the loop, yielding the given value
        Break(B),
    }

    #[unstable(feature = "control_flow_enum", reason = "new API", issue = "75744")]
    impl<B, C> Try for ControlFlow<B, C> {
        type Ok = C;
        type Error = B;
        #[inline]
        fn into_result(self) -> Result<Self::Ok, Self::Error> {
            match self {
                ControlFlow::Continue(y) => Ok(y),
                ControlFlow::Break(x) => Err(x),
            }
        }
        #[inline]
        fn from_error(v: Self::Error) -> Self {
            ControlFlow::Break(v)
        }
        #[inline]
        fn from_ok(v: Self::Ok) -> Self {
            ControlFlow::Continue(v)
        }
    }

    impl<B, C> ControlFlow<B, C> {
        /// Returns `true` if this is a `Break` variant.
        #[inline]
        #[unstable(feature = "control_flow_enum", reason = "new API", issue = "75744")]
        pub fn is_break(&self) -> bool {
            matches!(*self, ControlFlow::Break(_))
        }

        /// Returns `true` if this is a `Continue` variant.
        #[inline]
        #[unstable(feature = "control_flow_enum", reason = "new API", issue = "75744")]
        pub fn is_continue(&self) -> bool {
            matches!(*self, ControlFlow::Continue(_))
        }

        /// Converts the `ControlFlow` into an `Option` which is `Some` if the
        /// `ControlFlow` was `Break` and `None` otherwise.
        #[inline]
        #[unstable(feature = "control_flow_enum", reason = "new API", issue = "75744")]
        pub fn break_value(self) -> Option<B> {
            match self {
                ControlFlow::Continue(..) => None,
                ControlFlow::Break(x) => Some(x),
            }
        }

        /// Maps `ControlFlow<B, C>` to `ControlFlow<T, C>` by applying a function
        /// to the break value in case it exists.
        #[inline]
        #[unstable(feature = "control_flow_enum", reason = "new API", issue = "75744")]
        pub fn map_break<T, F>(self, f: F) -> ControlFlow<T, C>
        where
            F: FnOnce(B) -> T,
        {
            match self {
                ControlFlow::Continue(x) => ControlFlow::Continue(x),
                ControlFlow::Break(x) => ControlFlow::Break(f(x)),
            }
        }
    }

    impl<R: Try> ControlFlow<R, R::Ok> {
        /// Create a `ControlFlow` from any type implementing `Try`.
        #[unstable(feature = "control_flow_enum", reason = "new API", issue = "75744")]
        #[inline]
        pub fn from_try(r: R) -> Self {
            match Try::into_result(r) {
                Ok(v) => ControlFlow::Continue(v),
                Err(v) => ControlFlow::Break(Try::from_error(v)),
            }
        }

        /// Convert a `ControlFlow` into any type implementing `Try`;
        #[unstable(feature = "control_flow_enum", reason = "new API", issue = "75744")]
        #[inline]
        pub fn into_try(self) -> R {
            match self {
                ControlFlow::Continue(v) => Try::from_ok(v),
                ControlFlow::Break(v) => v,
            }
        }
    }

    impl<B> ControlFlow<B, ()> {
        /// It's frequently the case that there's no value needed with `Continue`,
        /// so this provides a way to avoid typing `(())`, if you prefer it.
        ///
        /// # Examples
        ///
        /// ```
        /// #![feature(control_flow_enum)]
        /// use std::ops::ControlFlow;
        ///
        /// let mut partial_sum = 0;
        /// let last_used = (1..10).chain(20..25).try_for_each(|x| {
        ///     partial_sum += x;
        ///     if partial_sum > 100 { ControlFlow::Break(x) }
        ///     else { ControlFlow::CONTINUE }
        /// });
        /// assert_eq!(last_used.break_value(), Some(22));
        /// ```
        #[unstable(feature = "control_flow_enum", reason = "new API", issue = "75744")]
        pub const CONTINUE: Self = ControlFlow::Continue(());
    }

    impl<C> ControlFlow<(), C> {
        /// APIs like `try_for_each` don't need values with `Break`,
        /// so this provides a way to avoid typing `(())`, if you prefer it.
        ///
        /// # Examples
        ///
        /// ```
        /// #![feature(control_flow_enum)]
        /// use std::ops::ControlFlow;
        ///
        /// let mut partial_sum = 0;
        /// (1..10).chain(20..25).try_for_each(|x| {
        ///     if partial_sum > 100 { ControlFlow::BREAK }
        ///     else { partial_sum += x; ControlFlow::CONTINUE }
        /// });
        /// assert_eq!(partial_sum, 108);
        /// ```
        #[unstable(feature = "control_flow_enum", reason = "new API", issue = "75744")]
        pub const BREAK: Self = ControlFlow::Break(());
    }