1 unstable release
Uses old Rust 2015
0.3.0 | Aug 11, 2016 |
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#24 in #tagged
11KB
169 lines
Same-size tagged data structure conversions
This crate provides a few boilerplate macros to enable conversions between types that are unions with a built-in discriminatory field. An example is a network protocol that consists of multiple packet-types with their respective packet-type indicated by a field on the struct:
#[repr(C)]
pub struct Packet {
packet_type: u8,
// an unknown (depends on packet type) payload
data: [u8; 7],
}
#[repr(C)]
pub struct StatusPacket {
/// must be 0x02 for a status packet
packet_type: u8,
status_0: u8,
status_1: u8,
status_2: u8,
ts: [u8; 4],
}
#[macro_use]
extern crate pcast;
pub enum ConversionError {
WrongPacketType
}
subtype_of!(Packet => StatusPacket | ConversionError {
Ok(())
});
The StatusPacket has three fields for various flags and a four byte timestamp here; its presence is indicated by a value of 0x02 in packet_type.
The subtype_of macro can now be used to declare express this. As a result, a Packet can be try_into'd into a StatusPacket and references can be passed because &StatusPacket will Deref to &Packet.
A conversion from &mut StatusPacket to &mut Packet is not included, as altering the Packet-structure might violate invariants required by StatusPacket.
Dependencies
~15KB