1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37

use std::marker;

use heed_traits::BoxedError;

/// Lazily decodes the data bytes.
///
/// It can be used to avoid CPU-intensive decoding before making sure that it
/// actually needs to be decoded (e.g. based on the key).
#[derive(Default)]
pub struct LazyDecode<C>(marker::PhantomData<C>);

impl<'a, C: 'static> heed_traits::BytesDecode<'a> for LazyDecode<C> {
    type DItem = Lazy<'a, C>;

    fn bytes_decode(bytes: &'a [u8]) -> Result<Self::DItem, BoxedError> {
        Ok(Lazy { data: bytes, _phantom: marker::PhantomData })
    }
}

/// Owns bytes that can be decoded on demand.
#[derive(Copy, Clone)]
pub struct Lazy<'a, C> {
    data: &'a [u8],
    _phantom: marker::PhantomData<C>,
}

impl<'a, C: heed_traits::BytesDecode<'a>> Lazy<'a, C> {
    /// Change the codec type of the given bytes, specifying the new codec.
    pub fn remap<NC>(&self) -> Lazy<'a, NC> {
        Lazy { data: self.data, _phantom: marker::PhantomData }
    }

    /// Decode the given bytes as `DItem`.
    pub fn decode(&self) -> Result<C::DItem, BoxedError> {
        C::bytes_decode(self.data)
    }
}