Macro dec_try

macro_rules! dec_try {
    ($result:expr, $offset:expr) => { ... };
    ($result:expr) => { ... };
    ($buf:expr, $offset:expr; $fun:expr) => { ... };
    ($buf:expr, $offset:expr; $fun:expr, $($args:expr),+) => { ... };
    ($buf:expr, $offset:expr; $object:expr; $fun:ident) => { ... };
    ($buf:expr, $offset:expr; $object:expr; $fun:ident, $($args:expr),+) => { ... };
    ($buf:expr; $($tts:tt)+) => { ... };
}

The decoding equivalent of enc_try. The only difference is that only an immutable borrow of the buffer is required each time.