Derive Macro Specifier 

#[derive(Specifier)]
{
    // Attributes available to this derive:
    #[bits]
}

Derive macro generating an impl of the trait Specifier.

This macro can be used on all unit enums and structs annotated with #[bitfield]. The enum or struct can be up to 128 bits in size; anything larger will cause a compilation error.

Options

• #[bits = N]: Explicitly specifies the number of bits used by a unit enum. This attribute is required when an enum does not have a power-of-two number of variants, but can be used for extra validation no matter what.

Examples

Basic usage

In this example, an extra variant (Invalid) is required because otherwise the enum would not contain a power-of-two number of variants. The power-of-two requirement ensures conversion from raw bits is infallible.

use modular_bitfield::prelude::*;

#[derive(Specifier)]
pub enum Weekday {
    Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday, Invalid
}

Using #[bits = N]

To eliminate the power-of-two requirement, add the #[bits] attribute:

#[derive(Specifier)]
#[bits = 3]
pub enum Weekday {
    Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday
}

Discriminants

Discriminants can be used normally to explicitly override certain values:

#[derive(Specifier)]
#[bits = 3]
pub enum Weekday {
    Monday = 1,
    Tuesday /* 2 … */,
    Wednesday,
    Thursday,
    Friday,
    Saturday,
    Sunday = 0,
}

With #[bitfield]

An enum that implements Specifier can be used normally as a field type in a #[bitfield] struct:

#[bitfield]
pub struct MeetingTimeSlot {
    day: Weekday,
    from: B6,
    to: B6,
    expired: bool,
}

let mut slot = MeetingTimeSlot::new()
    .with_day(Weekday::Friday)
    .with_from(14) // 14:00
    .with_to(15); // 15:00
assert_eq!(slot.day(), Weekday::Friday);
assert_eq!(slot.from(), 14);
assert_eq!(slot.to(), 15);
assert!(!slot.expired());