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try_len method #723

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merged 5 commits into from
Aug 9, 2023
Merged

try_len method #723

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5721f37
`try_len` method
Easyoakland Aug 7, 2023
6e54b0f
take by ref
Easyoakland Aug 7, 2023
952d8c4
match other `sizehint` function conventions
Easyoakland Aug 8, 2023
87ad574
Result not Option, inline, no Sized bound, improve docs
Easyoakland Aug 9, 2023
068de35
inline function source code and remove annotation
Easyoakland Aug 9, 2023
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24 changes: 24 additions & 0 deletions src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3840,6 +3840,30 @@ pub trait Itertools : Iterator {
{
MultiUnzip::multiunzip(self)
}

/// Returns the length of the iterator if one exists.
/// Otherwise return `self.size_hint()`.
///
/// Fallible [`ExactSizeIterator::len`].
///
/// Inherits guarantees and restrictions from [`Iterator::size_hint`].
///
/// ```
/// use itertools::Itertools;
///
/// assert_eq!([0; 10].iter().try_len(), Ok(10));
/// assert_eq!((10..15).try_len(), Ok(5));
/// assert_eq!((15..10).try_len(), Ok(0));
/// assert_eq!((10..).try_len(), Err((usize::MAX, None)));
/// assert_eq!((10..15).filter(|x| x % 2 == 0).try_len(), Err((0, Some(5))));
/// ```
fn try_len(&self) -> Result<usize, size_hint::SizeHint> {
let sh = self.size_hint();
match sh {
(lo, Some(hi)) if lo == hi => Ok(lo),
_ => Err(sh),
}
}
}

impl<T: ?Sized> Itertools for T where T: Iterator { }
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