6 releases
0.1.5 | Aug 30, 2019 |
---|---|
0.1.4 | Jun 12, 2019 |
0.1.3 | May 8, 2019 |
#71 in #newtype
Used in 2 crates
(via wasi-types)
18KB
351 lines
proper
Derives for converting primitives to and from simple enums and newtype structs. This crate is useful for converting between Rust and C representations.
Usage
Simple enums
A simple enum is one that does not have variants containing data. In other words, it's a
C-like/POD enum (as opposed to a tagged union).
Simple enums can be converted from unsigned integer types no larger than the min_ty
and to
unsigned integer types no smaller than the min_ty
.
The default min_ty
is the smallest type that can fit the number of enum variants.
For example, an enum with 255 variants would have min_ty = u8
but one with 256 would have
min_ty = u16
. The min_ty
can be configured using the #[prim(ty = "<min_ty>")]
attribute.
Example
#[macro_use]
extern crate proper;
use std::convert::TryFrom;
#[derive(Prim)]
enum EnumU8 {
Variant0,
Variant1,
}
#[derive(Prim)]
#[prim(ty = "u16")]
enum EnumU16 {
Variant0,
Variant1,
}
let e_u8 = EnumU8::try_from(42u8)?;
let e_u8 = EnumU8::try_from(42u16)?; // won't compile!
let e_u16 = EnumU16::try_from(42u16)?; // compiles!
let prim = e_u8 as u32;
let prim = e_u16 as u8;
Newtype structs
Newtype structs can be created from an integer type with the same sign and bitwidth
no larger than the contained type.
Inversely, newtype structs can be converted to any integer type with the same sign and bitwidth
as the contained type.
For instance, MyType(u16)
can be created from u8
and u16
but not u32
; and converted to
u16
and u32
, but not u8
.
Example
#[macro_use]
extern crate proper;
#[derive(Prim)]
struct FileDescriptor(u32);
let fd = FileDescriptor::from(42u8);
let prim: u16 = fd.into(); // won't compile!
let prim: u32 = fd.into();
let prim: u64 = fd.into();
Dependencies
~1.5MB
~36K SLoC