auto_impl

A simple compiler plugin for automatically implementing a trait for some common smart pointers and closures.

Usage

This library requires the nightly channel.

Add auto_impl to your Cargo.toml:

auto_impl = "*"

Reference in your crate root:

#![feature(proc_macro)]

extern crate auto_impl;

use auto_impl::auto_impl;

The following types are supported:

• Arc
• Rc
• Box
• Fn
• FnMut
• FnOnce
• &
• &mut

Implement a trait for a smart pointer

Add the #[auto_impl] attribute to traits to automatically implement them for wrapper types:

#[auto_impl(Arc, Box, Rc)]
trait MyTrait<'a, T> 
    where T: AsRef<str>
{
    type Type1;
    type Type2;

    fn execute1<'b>(&'a self, arg1: &'b T) -> Result<Self::Type1, String>;
    fn execute2(&self) -> Self::Type2;
}

Will expand to:

impl<'a, T, TAutoImpl> MyTrait<'a, T> for ::std::sync::Arc<TAutoImpl>
    where TAutoImpl: MyTrait<'a, T>,
          T: AsRef<str>
{
    type Type1 = TAutoImpl::Type1;
    type Type2 = TAutoImpl::Type2;

    fn execute1<'b>(&'a self, arg1: &'b T) -> Result<Self::Type1, String> {
        self.as_ref().execute1(arg1)
    }

    fn execute2(&self) -> Self::Type2 {
        self.as_ref().execute2()
    }
}

impl<'a, T, TAutoImpl> MyTrait<'a, T> for Box<TAutoImpl>
    where TAutoImpl: MyTrait<'a, T>,
          T: AsRef<str>
{
    type Type1 = TAutoImpl::Type1;
    type Type2 = TAutoImpl::Type2;

    fn execute1<'b>(&'a self, arg1: &'b T) -> Result<Self::Type1, String> {
        self.as_ref().execute1(arg1)
    }

    fn execute2(&self) -> Self::Type2 {
        self.as_ref().execute2()
    }
}

impl<'a, T, TAutoImpl> MyTrait<'a, T> for ::std::rc::Rc<TAutoImpl>
    where TAutoImpl: MyTrait<'a, T>,
          T: AsRef<str>
{
    type Type1 = TAutoImpl::Type1;
    type Type2 = TAutoImpl::Type2;

    fn execute1<'b>(&'a self, arg1: &'b T) -> Result<Self::Type1, String> {
        self.as_ref().execute1(arg1)
    }

    fn execute2(&self) -> Self::Type2 {
        self.as_ref().execute2()
    }
}

There are a few restrictions on #[auto_impl] for smart pointers. The trait must:

• Only have methods that take &self

Implement a trait for a closure

#[auto_impl(Fn)]
trait MyTrait<'a, T> {
    fn execute<'b>(&'a self, arg1: &'b T, arg2: &'static str) -> Result<(), String>;
}

Will expand to:

impl<'a, T, TAutoImpl> MyTrait<'a, T> for TAutoImpl
    where TAutoImpl: Fn(&T, &'static str) -> Result<(), String>
{
    fn execute<'b>(&'a self, arg1: &'b T, arg1: &'static str) -> Result<(), String> {
        self(arg1, arg2)
    }
}

There are a few restrictions on #[auto_impl] for closures. The trait must:

• Have a single method
• Have no associated types
• Have no non-static lifetimes in the return type

Implement a trait for a borrowed reference

#[auto_impl(&, &mut)]
trait MyTrait<'a, T> {
    fn execute<'b>(&'a self, arg1: &'b T, arg2: &'static str) -> Result<(), String>;
}

Will expand to:

impl<'auto, 'a, T, TAutoImpl> MyTrait<'a, T> for &'auto TAutoImpl {
    fn execute<'b>(&'a self, arg1: &'b T, arg1: &'static str) -> Result<(), String> {
        (**self).execute(arg1, arg2)
    }
}

impl<'auto, 'a, T, TAutoImpl> MyTrait<'a, T> for &'auto mut TAutoImpl {
    fn execute<'b>(&'a self, arg1: &'b T, arg1: &'static str) -> Result<(), String> {
        (**self).execute(arg1, arg2)
    }
}

There are a few restrictions on #[auto_impl] for immutably borrowed references. The trait must:

• Only have methods that take &self

There are no restrictions on #[auto_impl] for mutably borrowed references.