sort_by_derive 0.1.3

Derive macro SortBy and helper macros EnumAccessor and EnumSequence, deriving traits `Ord`, `PartialOrd`, `Eq`, `PartialEq` and `Hash` for structs and enums that can't automatically derive from those traits.
Documentation

sort_by_derive

This crate provides 3 derive macros SortBy, EnumAccessor and EnumSequence.

  • SortBy derives the traits Ord, PartialOrd, Eq, PartialEq and Hash on structs that can't automatically derive those traits because they contain unorderable fields such as f32.
  • On enums and structs, SortBy can also implement a Ord trait that calls arbitrary methods - this is particularly useful in combination with enum variant accessor methods derived by EnumAccessor an EnumSequence
  • EnumAccessor derives accessor methods to common fields in variants - so you don't need to write yourself match statements to access a field with the same name and type on different variants.
  • EnumSequence provides a enum_sequence method where the first variant returns 0, the second 1, etc. This is useful is you want to implement a custom sorting, while the order of declaration of variant is still relevant as a secondary ordering criteria.

Usage

SortBy

Fields that should be used for sorting are marked with the attribute #[sort_by]. Other fields will be ignored.

Alternatively, or in combination with, a struct-level or enum-level #[sort_by(method1(),method2())] can be declared. This top-level declaration takes precedence, fields comparison will be considered if method call comparison are eq.

Example

#[derive(SortBy)]
#[sort_by("somemethod()")]
struct Something {
    #[sort_by]
    a: u16,
    #[sort_by]
    c: u32,
    b: f32
}

will expand to:

impl std::hash::Hash for Something {
    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
        self.somemethod().hash(state);
        self.a.hash(state);
        self.c.hash(state);
    }
}
impl core::cmp::Eq for Something {}
impl core::cmp::PartialEq<Self> for Something {
    fn eq(&self, other: &Self) -> bool {
        self.cmp(other).is_eq()
    }
}
impl core::cmp::PartialOrd<Self> for Something {
    fn partial_cmp(
        &self,
        other: &Self,
    ) -> core::option::Option<core::cmp::Ordering> {
        std::option::Option::Some(self.cmp(other))
    }
}
impl core::cmp::Ord for Something {
    fn cmp(&self, other: &Self) -> core::cmp::Ordering {
        core::cmp::Ord::cmp(&self.somemethod(), &other.somemethod())
            .then_with(|| self.a.cmp(&other.a))
            .then_with(|| self.c.cmp(&other.c))
    }
}

EnumAccessor

Attributes are declared at top-level.

  • #[accessor(name: type)] will derive the accessor methods fn name(&self) -> &type; andfn name_mut(&mut self) -> &mut type;, and return a reference to the field of the same name on any variant.
  • #[accessor(name: type, (Exception1,Exception2))] derive the same accessor methods, but the return type will be Option<&type> and Option<&mut type>. The provided comma-separated list of variants are exceptions and will return None.

Example

Say we have a series of midi events, they are very similar but with slight variations - they always have some timing information but they may not always have a pitch or channel.

Using #[accessor(global_time: usize)], a global_time(&self) method is derived, along with a global_time_mut(&mut self), so without any boilerplate you can access the timing.

By declaring #[accessor(channel: u8, (CC))], channel(&self) and channel_mut(&mut self) are derived, but they return Some for NoteOn and NoteOff, and None for CC and Unsupported.

#[derive(EnumAccessor)]
#[accessor(global_time: usize)]
#[accessor(channel: u8, (CC))]
#[accessor(pitch: u8, (CC, Unsupported))]
enum Note {
    NoteOn(NoteOn),
    NoteOff(NoteOff),
    CC(CC),
    Unsupported {
        global_time: usize,
        rawdata: Vec<u8>
    }
}

expands to:

pub trait NoteAccessor {
    fn global_time(&self) -> &usize;
    fn global_time_mut(&mut self) -> &mut usize;
    fn channel(&self) -> std::option::Option<&u8>;
    fn channel_mut(&mut self) -> std::option::Option<&mut u8>;
    fn pitch(&self) -> std::option::Option<&u8>;
    fn pitch_mut(&mut self) -> std::option::Option<&mut u8>;
}
impl NoteAccessor for Note {
    fn global_time(&self) -> &usize {
        match self {
            Self::NoteOn(x) => &x.global_time,
            Self::NoteOff(x) => &x.global_time,
            Self::CC(x) => &x.global_time,
            Self::Unsupported { global_time, .. } => global_time,
        }
    }
    fn global_time_mut(&mut self) -> &mut usize {
        match self {
            Self::NoteOn(x) => &mut x.global_time,
            Self::NoteOff(x) => &mut x.global_time,
            Self::CC(x) => &mut x.global_time,
            Self::Unsupported { global_time, .. } => global_time,
        }
    }
    fn channel(&self) -> std::option::Option<&u8> {
        match self {
            Self::NoteOn(x) => std::option::Option::Some(&x.channel),
            Self::NoteOff(x) => std::option::Option::Some(&x.channel),
            Self::CC(x) => std::option::Option::Some(&x.channel),
            Self::Unsupported { .. } => std::option::Option::None,
        }
    }
    fn channel_mut(&mut self) -> std::option::Option<&mut u8> {
        match self {
            Self::NoteOn(x) => std::option::Option::Some(&mut x.channel),
            Self::NoteOff(x) => std::option::Option::Some(&mut x.channel),
            Self::CC(x) => std::option::Option::Some(&mut x.channel),
            Self::Unsupported { .. } => std::option::Option::None,
        }
    }
    fn pitch(&self) -> std::option::Option<&u8> {
        match self {
            Self::NoteOn(x) => std::option::Option::Some(&x.pitch),
            Self::NoteOff(x) => std::option::Option::Some(&x.pitch),
            Self::CC(_) => std::option::Option::None,
            Self::Unsupported { .. } => std::option::Option::None,
        }
    }
    fn pitch_mut(&mut self) -> std::option::Option<&mut u8> {
        match self {
            Self::NoteOn(x) => std::option::Option::Some(&mut x.pitch),
            Self::NoteOff(x) => std::option::Option::Some(&mut x.pitch),
            Self::CC(_) => std::option::Option::None,
            Self::Unsupported { .. } => std::option::Option::None,
        }
    }
}

EnumAccessor

Simply derive EnumSequence, and you get enum_sequence(&self) which returns a usize, starting from 0 and incrementing for each variant.

Example

#[derive(EnumSequence)]
enum ABC {
    A(u8),
    B(String),
    C{f: String, g: usize}
}

expands to

pub trait ABCEnumSequence {
    fn enum_sequence(&self) -> usize;
}
impl ABCEnumSequence for ABC {
    fn enum_sequence(&self) -> usize {
        match self {
            Self::A(..) => 0usize,
            Self::B(..) => 1usize,
            Self::C { .. } => 2usize,
        }
    }
}

All together

Imagine the following :

#[derive(EnumSequence, EnumAccessor, SortBy, Debug)]
#[accessor(global_time: usize)]
#[accessor(channel: u8, (CC))]
#[accessor(pitch: u8, (CC,SomethingElse))]
#[sort_by("global_time()", "channel()", "pitch()", "enum_sequence()")]
enum Note {
    NoteOn(NoteOn),
    NoteOff(NoteOff),
    CC(CC),
    SomethingElse {
        global_time: usize,
        channel: u8,
    }
}

Now I have a Note enum that will sort by global_time, channel, pitch, and lastly by variant order ( enum_sequence ). Note that None is always less than Some.

Conversely, separate structs such as NoteOn may derive from SortBy in order to ignore some fields ( ex: velocity may be a f32, so we can't directly derive Ord ).

Limitations

  • On unnamed variants, EnumAccessor only considers the first parameter.
  • struct-level sort_by attribute always come before field-level attributes.