[−][src]Crate num_enum
num_enum
Procedural macros to make inter-operation between primitives and enums easier. This crate is no_std compatible.
Turning an enum into a primitive
use num_enum::IntoPrimitive; #[derive(IntoPrimitive)] #[repr(u8)] enum Number { Zero, One, } fn main() { let zero: u8 = Number::Zero.into(); assert_eq!(zero, 0u8); }
num_enum
's IntoPrimitive
is more type-safe than using as
, because as
will silently truncate - num_enum
only derives From
for exactly the discriminant type of the enum.
Attempting to turn a primitive into an enum with try_from
use num_enum::TryFromPrimitive; use std::convert::TryFrom; #[derive(Debug, Eq, PartialEq, TryFromPrimitive)] #[repr(u8)] enum Number { Zero, One, } fn main() { let zero = Number::try_from(0u8); assert_eq!(zero, Ok(Number::Zero)); let three = Number::try_from(3u8); assert_eq!( three.unwrap_err().to_string(), "No discriminant in enum `Number` matches the value `3`", ); }
Unsafely turning a primitive into an enum with from_unchecked
If you're really certain a conversion will succeed, and want to avoid a small amount of overhead, you can use unsafe
code to do this conversion. Unless you have data showing that the match statement generated in the try_from
above is a
bottleneck for you, you should avoid doing this, as the unsafe code has potential to cause serious memory issues in
your program.
use num_enum::UnsafeFromPrimitive; #[derive(Debug, Eq, PartialEq, UnsafeFromPrimitive)] #[repr(u8)] enum Number { Zero, One, } fn main() { assert_eq!( Number::Zero, unsafe { Number::from_unchecked(0_u8) }, ); assert_eq!( Number::One, unsafe { Number::from_unchecked(1_u8) }, ); } unsafe fn undefined_behavior() { let _ = Number::from_unchecked(2); // 2 is not a valid discriminant! }
Optional features
Some enum values may be composed of complex expressions, for example:
enum Number { Zero = (0, 1).0, One = (0, 1).1, }
To cut down on compile time, these are not supported by default, but if you enable the complex-expressions
feature of your dependency on num_enum
, these should start working.
Structs
TryFromPrimitiveError |
Traits
TryFromPrimitive |
Derive Macros
IntoPrimitive | Implements |
TryFromPrimitive | Implements |
UnsafeFromPrimitive | Generates a |