Update docs for the API changes so far

README.md

@@ -46,7 +46,7 @@ fn main() {
 
 Target traits must be explicitly designated beforehand. There are three ways of doing it:
 
-## `#[cast_to]` to `impl` item
+### `#[cast_to]` to `impl` item
 The trait implemented is designated as a target trait.
 
 ```rust
@@ -63,7 +63,7 @@ impl Greet for Data {
 }
 ```
 
-## `#[cast_to(Trait)]` to type definition
+### `#[cast_to(Trait)]` to type definition
 For the type, the traits specified as arguments to the `#[cast_to(...)]` attribute are designated as target traits.
 
 ```rust
@@ -82,7 +82,7 @@ impl Greet for Data {
 struct Data;
 ```
 
-## `castable_to!(Type => Trait1, Trait2)`
+### `castable_to!(Type => Trait1, Trait2)`
 For the type, the traits following `:` are designated as target traits.
 
 ```rust
@@ -103,14 +103,22 @@ castable_to!(Data => Greet, std::fmt::Debug);
 fn main() {}
 ```
 
+## `Arc` Support
+`std::sync::Arc` is unique in that it implement `downcast` method only on `dyn Any + Send + Sync + 'static'.
+To use with `Arc`, the following steps should be taken:
+
+* Mark source traits with [`CastFromSync`] instead of [`CastFrom`]
+* Add `[sync]` flag to `#[cast_to]` and `castable_to!` as follows:
+  ```ignore
+  #[cast_to([sync])]
+  #[cast_to([sync] Trait1, Trait2)]
+  castable_to!(Type => [sync] Trait, Trait2);
+  ```
+
 # How it works
 First of all, [`CastFrom`] trait makes it possible to retrieve an object of [`std::any::Any`]
 from an object for a sub-trait of [`CastFrom`]. 
 
-> [`CastFrom`] will become obsolete and be replaced with [`std::any::Any`]
-> once [unsized coercion](https://doc.rust-lang.org/reference/type-coercions.html#unsized-coercions)
-> from a trait object to another trait object for its super-trait is implemented in the stable Rust.
-
 And the macros provided by `intertrait` generates trampoline functions for downcasting a trait object
 for [`std::any::Any`] back to its concrete type and then creating a trait object for the target trait from it.
 
@@ -143,4 +151,5 @@ dual licensed as above, without any additional terms or conditions.
 
 [`std::any::Any`]: https://doc.rust-lang.org/std/any/trait.Any.html
 [`TypeId`]: https://doc.rust-lang.org/std/any/struct.TypeId.html
-[`CastFrom`]: https://docs.rs/intertrait/*/intertrait/trait.CastFrom.html
+[`CastFrom`]: https://docs.rs/intertrait/*/intertrait/trait.CastFrom.html
+[`CastFromSync`]: https://docs.rs/intertrait/*/intertrait/trait.CastFromSync.html

macros/src/lib.rs

@@ -17,6 +17,9 @@ mod item_type;
 /// If on an `impl` item, no argument is allowed. But on a type definition, the target traits
 /// must be listed explicitly.
 ///
+/// Add `[sync]` before the list of traits if the underlying type is `Sync + Send` and you
+/// need `std::sync::Arc`.
+///
 /// # Examples
 /// ## On a trait impl
 /// ```
@@ -43,6 +46,15 @@ mod item_type;
 /// #[derive(std::fmt::Debug)]
 /// struct Data;
 /// ```
+///
+/// ## For Arc
+/// Use when the underlying type is `Sync + Send` and you want to use `Arc`.
+/// ```
+/// // Debug can be cast into from any sub-trait of CastFrom implemented by Data
+/// #[cast_to([sync] std::fmt::Debug)]
+/// #[derive(std::fmt::Debug)]
+/// struct Data;
+/// ```
 #[proc_macro_attribute]
 pub fn cast_to(args: TokenStream, input: TokenStream) -> TokenStream {
     match parse::<Targets>(args) {
@@ -60,7 +72,7 @@ pub fn cast_to(args: TokenStream, input: TokenStream) -> TokenStream {
     .into()
 }
 
-/// Declare target traits for casting implemented by a type.
+/// Declares target traits for casting implemented by a type.
 ///
 /// This macro is for registering both a concrete type and its traits to be targets for casting.
 /// Useful when the type definition and the trait implementations are in an external crate.
@@ -84,6 +96,23 @@ pub fn cast_to(args: TokenStream, input: TokenStream) -> TokenStream {
 /// }
 /// castable_to! { Data => std::fmt::Debug, Greet }
 /// ```
+///
+/// When the type is `Sync + Send` and is used with `Arc`:
+/// ```
+/// #[derive(std::fmt::Debug)]
+/// enum Data {
+///     A, B, C
+/// }
+/// trait Greet {
+///     fn greet(&self);
+/// }
+/// impl Greet for Data {
+///     fn greet(&self) {
+///         println!("Hello");
+///     }
+/// }
+/// castable_to! { Data => [sync] std::fmt::Debug, Greet }
+/// ```
 #[proc_macro]
 pub fn castable_to(input: TokenStream) -> TokenStream {
     let Casts {

src/cast.rs

@@ -1,3 +1,13 @@
+//! `cast` module contains traits to provide `cast` method for various references
+//! and smart pointers.
+//!
+//! In source files requiring casts, import all of the traits as follows:
+//!
+//! ```ignore
+//! use intertrait::cast::*;
+//! ```
+//!
+//! Since there exists single trait for each receiver type, the same `cast` method is overloaded.
 mod cast_arc;
 mod cast_box;
 mod cast_mut;

src/lib.rs

@@ -1,6 +1,6 @@
 //! A library providing direct casting among trait objects implemented by a type.
 //!
-//! In Rust, an object of a sub-trait of [`std::any::Any`] can be downcast to a concrete type
+//! In Rust, an object of a sub-trait of [`Any`] can be downcast to a concrete type
 //! at runtime if the type is known. But no direct casting between two trait objects
 //! (i.e. without involving the concrete type of the backing value) are possible
 //! (even no coercion from a trait object to that of its super-trait yet).
@@ -45,14 +45,19 @@
 //! * [`#[cast_to(Trait)]`][cast_to] to type definition
 //! * [`castable_to!(Type => Trait1, Trait2)`][castable_to]
 //!
-//! Refer to the documents for each of macros for details.
+//! If the underlying type involved is `Sync + Send` and you want to use it with [`Arc`],
+//! use [`CastFromSync`] in place of [`CastFrom`] and add `[sync]` flag before the list
+//! of traits in the macros. Refer to the documents for each of macros for details.
 //!
 //! For casting, refer to traits defined in [`cast`] module.
 //!
 //! [cast_to]: ./attr.cast_to.html
 //! [castable_to]: ./macro.castable_to.html
+//! [`CastFrom`]: ./trait.CastFrom.html
+//! [`CastFromSync`]: ./trait.CastFromSync.html
 //! [`cast`]: ./cast/index.html
 //! [`Any`]: https://doc.rust-lang.org/std/any/trait.Any.html
+//! [`Arc`]: https://doc.rust-lang.org/std/sync/struct.Arc.html
 use std::any::{Any, TypeId};
 use std::collections::HashMap;
 use std::rc::Rc;