Use existing types in an enum in Rust

Question

Say I have two structs:

struct BlankDoc {
    width: u32,
    height: u32
}

struct UrlDoc<'a> {
    url: &str<'a>
}

Is there some way to use enums to make a Doc type that will be either a BlankDoc or a UrlDoc, without having to reimplement (copy) all of their fields?

I was thinking something like this:

enum Doc {
    &BlankDoc
    &UrlDoc
}

or

type Doc = BlankDoc|UrlDoc;

(Obviously neither of these ways exist.)

What's the idiomatic way to model this in Rust?

Answer 1

You can wrap the existing structs in an enum. Eg

enum Doc<'a> {
    Blank(BlankDoc),
    Url(UrlDoc<'a>),
}

then you can do for instance:

fn test<'a>(doc: Doc<'a>) {
    match doc {
        Doc::Blank( BlankDoc { width: w, height: h }) =>
            println!("BlankDoc with w:{}, h:{}", w, h),
        Doc::Url( UrlDoc { url: u }) =>
            println!("UrlDoc with url:{}", u),
    }
}

full playground example