//! Contains a borrowed Object bound to a buffer holding its decompressed data. use crate::{BlobRef, CommitRef, CommitRefIter, Data, Kind, ObjectRef, TagRef, TagRefIter, TreeRef, TreeRefIter}; impl<'a> Data<'a> {    /// Constructs a new data object from `kind` and `data`.    pub fn new(kind: Kind, data: &'a [u8]) -> Data<'a> {        Data { kind, data }    }    /// Decodes the data in the backing slice into a [`ObjectRef`], allowing to access all of its data    /// conveniently. The cost of parsing an object is negligible.    ///    /// **Note** that [mutable, decoded objects][crate::Object] can be created from [`Data`]    /// using [`crate::ObjectRef::into_owned()`].    pub fn decode(&self) -> Result<ObjectRef<'a>, crate::decode::Error> {        Ok(match self.kind {            Kind::Tree => ObjectRef::Tree(TreeRef::from_bytes(self.data)?),            Kind::Blob => ObjectRef::Blob(BlobRef { data: self.data }),            Kind::Commit => ObjectRef::Commit(CommitRef::from_bytes(self.data)?),            Kind::Tag => ObjectRef::Tag(TagRef::from_bytes(self.data)?),        })    }     /// Returns this object as tree iterator to parse entries one at a time to avoid allocations, or    /// `None` if this is not a tree object.    pub fn try_into_tree_iter(self) -> Option<TreeRefIter<'a>> {        match self.kind {            Kind::Tree => Some(TreeRefIter::from_bytes(self.data)),            _ => None,        }    }     /// Returns this object as commit iterator to parse tokens one at a time to avoid allocations, or    /// `None` if this is not a commit object.    pub fn try_into_commit_iter(self) -> Option<CommitRefIter<'a>> {        match self.kind {            Kind::Commit => Some(CommitRefIter::from_bytes(self.data)),            _ => None,        }    }     /// Returns this object as tag iterator to parse tokens one at a time to avoid allocations, or    /// `None` if this is not a tag object.    pub fn try_into_tag_iter(self) -> Option<TagRefIter<'a>> {        match self.kind {            Kind::Tag => Some(TagRefIter::from_bytes(self.data)),            _ => None,        }    }} /// Types supporting object hash verificationpub mod verify {    use quick_error::quick_error;     quick_error! {        /// Returned by [`crate::Data::verify_checksum()`]        #[derive(Debug)]        #[allow(missing_docs)]        pub enum Error {            ChecksumMismatch {desired: git_hash::ObjectId, actual: git_hash::ObjectId} {                display("Object expected to have id {}, but actual id was {}", desired, actual)            }        }    }     impl crate::Data<'_> {        /// Compute the checksum of `self` and compare it with the `desired` hash.        /// If the hashes do not match, an [`Error`] is returned, containing the actual        /// hash of `self`.        pub fn verify_checksum(&self, desired: impl AsRef<git_hash::oid>) -> Result<(), Error> {            let desired = desired.as_ref();            let mut hasher = git_features::hash::hasher(desired.kind());            hasher.update(&crate::encode::loose_header(self.kind, self.data.len()));            hasher.update(self.data);             let actual_id = git_hash::ObjectId::from(hasher.digest());            if desired != actual_id {                return Err(Error::ChecksumMismatch {                    desired: desired.into(),                    actual: actual_id,                });            }            Ok(())        }    }} #[cfg(test)]mod tests {    use super::*;     #[test]    fn size_of_object() {        assert_eq!(std::mem::size_of::<Data<'_>>(), 24, "this shouldn't change unnoticed");    }}