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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),
}
}
}
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(());
}
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