1 unstable release
0.1.0 | Jul 28, 2023 |
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#1329 in Rust patterns
185KB
275 lines
Hereditary
Procedural macros for emulating OOP Inheritance in Rust, by extending the trait functionality in structs based on their composition (as they contain instances of other types that implement the desired functionality).
Hereditary
generates the boilerplate of trait implementations for the composited struct,
by Forwarding the
required methods that wrap the functionality already implemented in the contained instances referenced by its struct fields.
Currently, Hereditary
support 2 kinds of delegation:
- Partial Delegation: By using the decorator attribute
#[forward_trait(submember)]
on trait implementations. - Full Delegation: By applying
#[derive(Forwarding)]
on the composited struct, it derives the trait implementation on the struct field (designated by attribute#[forward_derive(Trait)]
).
Note
Learn more in the documentation page here https://docs.rs/hereditary
Features
- Brings subtype polymorphism on composite structs with just one instruction, vesting the new type with the same interface as its components.
- Re-use fields/method implementations from other types as subcomponents, without needing to repeately write wrapping code that forwards the methods of those subcomponents.
Hereditary
tools are essentially zero-cost abstractions. They doesn't require runtime structures for holding trait type information. All the work it's done by macros and code generation.- Embrace the New Type pattern effectively, but without the previous
awkward issues of having to re-implement the
inner-type
interfaces for thenew-type
. By using this technique Rust programmers avoid the problems of incorporating new behaviour of existing foreign types, bypassing the Orphan Rule for traits.
Usage
Install in your repository:
cargo add hereditary
Insert hereditary
macros in your code:
mod animal {
// Attribute macro for generating trait info
#[hereditary::trait_info]
pub trait Cannis {
fn bark(&self)-> String;
fn sniff(&self)-> bool;
}
#[hereditary::trait_info]
pub trait Bird {
fn sing(&self) -> String;
fn fly(&mut self, elevation:f64) -> f64;
}
}
// Heritance for an hybrid animal
#[derive(hereditary::Forwarding)]
struct KimeraSphinx
{
#[forward_derive(animal::Cannis)] // full implementation of Cannis
dogpart:Bulldog,
birdpart:Seagull
}
// Combining existing trait implementation from Seagull instance
#[hereditary::forward_trait(birdpart)]
impl animal::Bird for KimeraSphinx
{
fn sing(&self) -> String
{
self.dogpart.bark()
}
}
// -- Subcomponent implementations -- //
struct Bulldog { position:f64 }
impl animal::Cannis for Bulldog {
//... Cannis methods ...
}
struct Seagull { elevation:f64 }
impl animal::Bird for Seagull {
//... Bird methods ...
}
fn main() {
// Instance kimera
let mut kimera = KimeraSphinx::new();
// A dogs that flies.
assert_eq!(kimera.fly(50f64), 50f64);
assert_eq!(kimera.bark(), kimera.sing()); // It barks instead of singing
assert_eq!(kimera.sniff(), true);
}
Limitations
- Because of the heavily usage of macros, code made with
Hereditary
would incurr in longer compilation processes. - Sometimes, the traits information cannot be referenced by external modules, because
trait_info
generated macros aren't imported automatically as same as their corresponding traits. That's why they need to be referenced with the full path in the forwarding attributes (animal::Bird
), instead of justBird
. This is a known issue related with declarative macros and the scope rules for their visibibility, as they have special needs when exporting them as module symbols.
License
Apache 2.0
Authors: Francisco Leon
Dependencies
~1.4–2MB
~26K SLoC