Crate proc_bitfield

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Expand description

proc-bitfield

A Rust crate to expressively declare bitfield-like structs, automatically ensuring their correctness at compile time and declaring accessors.

Automatic trait implementations

After the struct’s name and its storage type declaration, a list of automatic trait implementations can be optionally added. For example, the following declaration will result in all automatic implementations being applied:

bitfield! {
    pub struct Example(pub u8): Debug, FromRaw, IntoRaw, DerefRaw { ... }
}

Currently, the allowed automatic implementations are Debug, FromRaw, IntoRaw and DerefRaw.

Debug

If specified, core::fmt::Debug will be implemented automatically for the current bitfield struct; the generated fmt function will output the type’s raw value as well as all of its readable fields’ values.

FromRaw

If specified, core::convert::From<$storage_ty> will be implemented automatically for the current bitfield struct; the generated from function will construct an instance of the bitfield struct from the provided value directly, with no additional checks, analogously to $bitfield_ty(raw) in a context where the bitfield struct’s raw value field is accessible. This does not check or change the previously declared visibility of the bitfield struct’s raw value field (bitfield.0), or any other such manually-declared fields, so care must be taken to maintain consistency.

IntoRaw

If specified, core::convert::From<$bitfield_ty> will be implemented automatically for the current bitfield struct’s storage type (and consequently, core::convert::Into<$storage_ty> for the bitfield type); the generated from function will read the bitfield’s raw value, with no additional changes, analogously to bitfield.0 in a context where the bitfield struct’s raw value field is accessible. Analogously to FromRaw, care must be taken to maintain consistency with the visibility of the bitfield struct’s raw value outside this implementation.

DerefRaw

If specified, core::ops::Deref will be implemented automatically for the current bitfield struct; the generated deref function will read the bitfield’s raw value directly, analogously to &bitfield.0 in a context where the bitfield struct’s raw value field is accessible. Analogously to FromRaw, care must be taken to maintain consistency with the visibility of the bitfield struct’s raw value outside this implementation.

nightly feature and const fn accessors

NOTE: For now, the nightly feature is disabled as const trait functionality has been removed from the standard library in order to be reworked. For more info, read https://github.com/rust-lang/rust/pull/110393. The original description follows.

Optionally, the nightly feature can be enabled to use const Trait functionality: this makes the BitRange and Bit traits be implemented using const fns for all integer types, and enables the option to use const fns for field accessors.

With the feature enabled, const fn accessors can be enabled globally for a struct by replacing struct with const struct (i.e. const struct Example(pub u16)), or on a field-by-field basis by prepending const to its type (i.e. raw: const u16 @ ..).

Field declarations

Fields can be declared by using the form:

Visibility IDENTIFIER : Type ([(Option ,)* Option])? @ FieldRange

where FieldRange corresponds to any of (where L is an alias for LiteralExpression):

  • .., to use every bit
  • L..=L, to use the bits specified by an inclusive range
  • L..L, to use the bits specified by an exclusive range
  • L; L, to use bits specified by a (start, length) pair
  • L, to use a single bit; unlike all other specifications, this is only valid for bool fields, and will use the Bit trait instead of BitRange

Options can be optionally specified in brackets, matching any of the ones defined below.

Access restrictions

Fields are both readable and writable by default, but can be declared read-only or write-only using respectively the read_only/ro and write_only/wo options.

Field type conversions

Fields’ “raw” types as specified after the colon are restricted by BitRange<T> implementations on the bitfield’s contained type; however, accessors can perform conversions specified through optional options. These can be:

  • Infallible conversions, using the From<T> and Into<T> traits, the relevant options being:
    • get Type, specifying the type that the raw value will be converted into on reads, using From<T>
    • set Type, specifying the type that will be converted into the raw value on writes, using Into<T>
    • Type, as a shorthand for get Type and set Type
  • Fallible conversions, using the TryFrom<T> and TryInto<T> traits, the relevant options being:
    • try_get Type, specifying the type that the raw value will be fallibly converted into on reads, using TryFrom<T>
    • try_set Type, specifying the type that will be fallibly converted into the raw value on writes, using TryInto<T>
    • try_both Type, as a shorthand for try_get Type and try_set Type
    • try Type, as a shorthand for try_get Type and set Type
  • Unsafe conversions, using the UnsafeFrom<T> and UnsafeInto<T> traits, the relevant options being:
    • unsafe_get Type, specifying the type that the raw value will be unsafely converted into on reads, using UnsafeFrom<T>
    • unsafe_set Type, specifying the type that will be unsafely converted into the raw value on writes, using UnsafeInto<T>
    • unsafe_both Type, as shorthand for unsafe_get Type and unsafe_set Type
    • unsafe Type, as shorthand for unsafe_get Type and set Type

Modules

  • example
    Sample bitfields to showcase the crate’s features

Macros

Traits