farena 0.2.0

A file-backed arena allocator using pread for RSS-conscious byte storage
Documentation 
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/// Location of stored bytes within a [`crate::FileArena`].
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, Hash)]
pub struct Location {
    pub file_index: u16,
    pub offset: u32,
    pub len: u32,
}

impl Location {
    /// Creates a new `Location`, panicking if offset or len exceed `u32::MAX`.
    pub fn new(file_index: u16, offset: usize, len: usize) -> Self {
        Self {
            file_index,
            offset: u32::try_from(offset)
                .expect("Location: offset exceeds u32::MAX (4GB file limit)"),
            len: u32::try_from(len).expect("Location: len exceeds u32::MAX (4GB file limit)"),
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    #[should_panic(expected = "offset exceeds u32::MAX")]
    fn new_panics_on_large_offset() {
        Location::new(0, u32::MAX as usize + 1, 10);
    }

    #[test]
    #[should_panic(expected = "len exceeds u32::MAX")]
    fn new_panics_on_large_len() {
        Location::new(0, 10, u32::MAX as usize + 1);
    }

    #[test]
    fn test_location_eq() {
        let loc1 = Location::new(0, 100, 50);
        let loc2 = Location::new(0, 100, 50);
        let loc3 = Location::new(1, 100, 50);
        assert_eq!(loc1, loc2);
        assert_ne!(loc1, loc3);
    }

    #[test]
    fn test_location_hash() {
        use std::collections::HashSet;
        let loc1 = Location::new(0, 100, 50);
        let loc2 = Location::new(0, 100, 50);
        let loc3 = Location::new(1, 100, 50);
        let mut set = HashSet::new();
        set.insert(loc1);
        assert!(set.contains(&loc2));
        assert!(!set.contains(&loc3));
    }
}