Add Fields::iter_member

[Fancyflame]

Acts like Fields::iter, but map its Field items to Member.

For instance, in this struct

struct Foo {
    a: f32,
    b: bool
}

We use iter_member to access its fields, and implement Clone for it.

let fields: Fields = ...;
let idents = fields.iter().map(|f| &f.ident);
let members = fields.iter_member();
quote! {
    impl Clone for Foo {
        fn clone(&self) -> Self {
            Self {
                #(#idents: self.#members.clone(),)*
            }
        }
    }
}

Then it generates

impl Clone for Foo {
    fn clone(&self) -> Self {
        Self {
            a: self.a.clone(),
            b: self.b.clone(),
        }
    }
}

There is a similar effect on unnamed fields in which iterates Member::Index instead.

[programmerjake]

this type should be publicly accessible ... so probably don't put it in its own private module

[Fancyflame]

I have also considered this issue before, but I noticed that many iterator function s under Generics also return private types. What do you think?

[dtolnay]

Thanks!