Types should implement AsRef for themself

[Pauan]

Motivation

I'm working on porting dominator to use wasm-bindgen, and I ran into this big issue.

Dominator contains a struct DomBuilder<A> which allows it to work on any type. Then I implement methods only for certain types:

impl<A> DomBuilder<A> where A: AsRef<Node> {
    pub fn children(...) { ... }
    ...
}

impl<A> DomBuilder<A> where A: AsRef<Element> {
    pub fn class(...) { ... }
    ...
}

impl<A> DomBuilder<A> where A: AsRef<HtmlElement> {
    pub fn style(...) { ... }
    ...
}

The idea is that you can use DomBuilder on any type, but at compile-time it will statically restrict which methods you can use depending on the type.

So you can't use HtmlElement methods on a Node, for example. But you can use Node methods on a Node, Element, or HtmlElement.

This works great in stdweb, but it doesn't work in wasm-bindgen, because wasm-bindgen implements these...

impl AsRef<JsValue> for HtmlElement
impl AsRef<Object> for HtmlElement
impl AsRef<EventTarget> for HtmlElement
impl AsRef<Node> for HtmlElement
impl AsRef<Element> for HtmlElement

...but it does not implement impl AsRef<HtmlElement> for HtmlElement

That's a big problem, since it means that you cannot write code which is generic over the type.

Proposed Solution

Implement impl AsRef<Foo> for Foo for all types created by the #[wasm_bindgen] macro.

Alternatives

• Create a new trait that is similar to AsRef (seems redundant).

• Don't do this (makes writing generic code impossible).

Additional Context

There is precedence for this, since the stdlib defines these:

impl AsRef<CStr> for CStr
impl AsRef<OsStr> for OsStr
impl AsRef<Path> for Path
impl<T> AsRef<Vec<T>> for Vec<T>

And wasm-bindgen itself defines impl AsRef<JsValue> for JsValue