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/// A macro for creating iterators that can have statically known | ||
/// different types. Useful for iterating over tree children, where | ||
/// each tree node variant yields a different iterator type. | ||
#[macro_export] | ||
macro_rules! multi_iterator { | ||
($Iter:ident { $($Variant:ident),* $(,)? }) => { | ||
#[derive(Debug, Clone)] | ||
enum $Iter<$($Variant),*> { | ||
$($Variant { iter: $Variant }),* | ||
} | ||
|
||
impl<$($Variant),*> $Iter<$($Variant),*> { | ||
$( | ||
#[allow(non_snake_case)] | ||
fn $Variant(iter: impl IntoIterator<IntoIter = $Variant>) -> Self { | ||
$Iter::$Variant { iter: iter.into_iter() } | ||
} | ||
)* | ||
} | ||
|
||
impl<T, $($Variant: Iterator<Item = T>),*> Iterator for $Iter<$($Variant),*> { | ||
type Item = T; | ||
fn next(&mut self) -> Option<T> { | ||
match self { $($Iter::$Variant { iter } => iter.next()),* } | ||
} | ||
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fn size_hint(&self) -> (usize, Option<usize>) { | ||
match self { $($Iter::$Variant { iter } => iter.size_hint()),* } | ||
} | ||
} | ||
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impl<T, $($Variant: DoubleEndedIterator<Item = T>),*> DoubleEndedIterator for $Iter<$($Variant),*> { | ||
fn next_back(&mut self) -> Option<T> { | ||
match self { $($Iter::$Variant { iter } => iter.next_back()),* } | ||
} | ||
} | ||
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impl<T, $($Variant: ExactSizeIterator<Item = T>),*> ExactSizeIterator for $Iter<$($Variant),*> {} | ||
}; | ||
} |