rust - 使用 syn 时如何从 Option 获取 T？

Question

我正在使用 syn解析 Rust 代码。当我使用 field.ty 读取命名字段的类型时, 我得到一个 syn::Type .当我使用 quote!{#ty}.to_string() 打印它时我得到 "Option<String>" .

我怎样才能得到 "String" ？我想用 #ty在quote!打印 "String"而不是 "Option<String>" .

我想生成如下代码:

impl Foo {
    pub set_bar(&mut self, v: String) {
        self.bar = Some(v);
    }
}

开始于

struct Foo {
    bar: Option<String>
}

我的尝试:

let ast: DeriveInput = parse_macro_input!(input as DeriveInput);

let data: Data = ast.data;

match data {
    Data::Struct(ref data) => match data.fields {
        Fields::Named(ref fields) => {

            fields.named.iter().for_each(|field| {
                let name = &field.ident.clone().unwrap();

                let ty = &field.ty;
                quote!{
                    impl Foo {
                        pub set_bar(&mut self, v: #ty) {
                            self.bar = Some(v);
                        }
                    }
                };      
            });
        }
        _ => {}
    },
    _ => panic!("You can derive it only from struct"),
}

Answer 1

我的更新版本 the response from @Boiethios ，在公共(public) crate 中测试和使用，支持 Option 的多种语法:

• 选项
• std::option::Option
• ::std::option::Option
• 核心::选项::选项
• ::core::option::Option

fn extract_type_from_option(ty: &syn::Type) -> Option<&syn::Type> {
    use syn::{GenericArgument, Path, PathArguments, PathSegment};

    fn extract_type_path(ty: &syn::Type) -> Option<&Path> {
        match *ty {
            syn::Type::Path(ref typepath) if typepath.qself.is_none() => Some(&typepath.path),
            _ => None,
        }
    }

    // TODO store (with lazy static) the vec of string
    // TODO maybe optimization, reverse the order of segments
    fn extract_option_segment(path: &Path) -> Option<&PathSegment> {
        let idents_of_path = path
            .segments
            .iter()
            .into_iter()
            .fold(String::new(), |mut acc, v| {
                acc.push_str(&v.ident.to_string());
                acc.push('|');
                acc
            });
        vec!["Option|", "std|option|Option|", "core|option|Option|"]
            .into_iter()
            .find(|s| &idents_of_path == *s)
            .and_then(|_| path.segments.last())
    }

    extract_type_path(ty)
        .and_then(|path| extract_option_segment(path))
        .and_then(|path_seg| {
            let type_params = &path_seg.arguments;
            // It should have only on angle-bracketed param ("<String>"):
            match *type_params {
                PathArguments::AngleBracketed(ref params) => params.args.first(),
                _ => None,
            }
        })
        .and_then(|generic_arg| match *generic_arg {
            GenericArgument::Type(ref ty) => Some(ty),
            _ => None,
        })
}