Enum png::encoder::Wrapper

enum Wrapper<'a, W: Write> {
    Chunk(ChunkWriter<'a, W>),
    Zlib(ZlibEncoder<ChunkWriter<'a, W>>),
    Unrecoverable,
    None,
}

This enum is used to be allow the StreamWriter to keep its inner ChunkWriter without wrapping it inside a ZlibEncoder. This is used in the case that between the change of state that happens when the last write of a frame is performed an error occurs, which obviously has to be returned. This creates the problem of where to store the writer before exiting the function, and this is where Wrapper comes in.

Unfortunately the ZlibWriter can’t be used because on the write following the error, finish would be called and that would write some data even if 0 bytes where compressed.

If the finish function fails then there is nothing much to do as the ChunkWriter would get lost so the Unrecoverable variant is used to signal that.

Variants

Chunk(ChunkWriter<'a, W>)

Zlib(ZlibEncoder<ChunkWriter<'a, W>>)

Unrecoverable

None

This is used in-between, should never be matched

Implementations

impl<'a, W: Write> Wrapper<'a, W>

fn take(&mut self) -> Wrapper<'a, W>

Like Option::take this returns the Wrapper contained in self and replaces it with Wrapper::None