rust - 在 Rust 中派生实例时的多个 impl 候选者

Question

在 Rust 1.7 中尝试使用 rustc-serialize 对包含两个 String 的 struct 进行 (d)e(n) 编码时，编译器提示有太多 impl 候选项，不知道该选择哪一个。

代码:

#[derive(RustcDecodable, RustcEncodable, Debug)]
struct gonet {
    ip: String,
    mask: String,
}

投诉:

src/bin/measurer.rs:18:5: 18:15 error: multiple applicable items in scope [E0034]
src/bin/measurer.rs:18     ip: String,
                           ^~~~~~~~~~
src/bin/measurer.rs:16:26: 16:40 note: in this expansion of #[derive_RustcEncodable] (defined in src/bin/measurer.rs)
src/bin/measurer.rs:18:5: 18:15 help: run `rustc --explain E0034` to see a detailed explanation
src/bin/measurer.rs:18:5: 18:15 note: candidate #1 is defined in an impl of the trait `rustc_serialize::serialize::Encodable` for the type `str`
src/bin/measurer.rs:18     ip: String,
                           ^~~~~~~~~~
src/bin/measurer.rs:16:26: 16:40 note: in this expansion of #[derive_RustcEncodable] (defined in src/bin/measurer.rs)
src/bin/measurer.rs:18:5: 18:15 note: candidate #2 is defined in an impl of the trait `rustc_serialize::serialize::Encodable` for the type `collections::string::String`
src/bin/measurer.rs:18     ip: String,
                           ^~~~~~~~~~
src/bin/measurer.rs:16:26: 16:40 note: in this expansion of #[derive_RustcEncodable] (defined in src/bin/measurer.rs)
src/bin/measurer.rs:18:5: 18:15 note: candidate #3 is defined in an impl of the trait `rustc_serialize::serialize::Encodable` for the type `&_`
src/bin/measurer.rs:18     ip: String,
                           ^~~~~~~~~~
src/bin/measurer.rs:16:26: 16:40 note: in this expansion of #[derive_RustcEncodable] (defined in src/bin/measurer.rs)
src/bin/measurer.rs:18:5: 18:15 note: candidate #4 is defined in an impl of the trait `radix_trie::keys::TrieKey` for the type `_`
src/bin/measurer.rs:18     ip: String,
                           ^~~~~~~~~~
src/bin/measurer.rs:16:26: 16:40 note: in this expansion of #[derive_RustcEncodable] (defined in src/bin/measurer.rs)
src/bin/measurer.rs:19:5: 19:17 error: multiple applicable items in scope [E0034]
src/bin/measurer.rs:19     mask: String,
                           ^~~~~~~~~~~~
src/bin/measurer.rs:16:26: 16:40 note: in this expansion of #[derive_RustcEncodable] (defined in src/bin/measurer.rs)
src/bin/measurer.rs:19:5: 19:17 help: run `rustc --explain E0034` to see a detailed explanation
src/bin/measurer.rs:19:5: 19:17 note: candidate #1 is defined in an impl of the trait `rustc_serialize::serialize::Encodable` for the type `str`
src/bin/measurer.rs:19     mask: String,
                           ^~~~~~~~~~~~
src/bin/measurer.rs:16:26: 16:40 note: in this expansion of #[derive_RustcEncodable] (defined in src/bin/measurer.rs)
src/bin/measurer.rs:19:5: 19:17 note: candidate #2 is defined in an impl of the trait `rustc_serialize::serialize::Encodable` for the type `collections::string::String`
src/bin/measurer.rs:19     mask: String,
                           ^~~~~~~~~~~~
src/bin/measurer.rs:16:26: 16:40 note: in this expansion of #[derive_RustcEncodable] (defined in src/bin/measurer.rs)
src/bin/measurer.rs:19:5: 19:17 note: candidate #3 is defined in an impl of the trait `rustc_serialize::serialize::Encodable` for the type `&_`
src/bin/measurer.rs:19     mask: String,
                           ^~~~~~~~~~~~
src/bin/measurer.rs:16:26: 16:40 note: in this expansion of #[derive_RustcEncodable] (defined in src/bin/measurer.rs)
src/bin/measurer.rs:19:5: 19:17 note: candidate #4 is defined in an impl of the trait `radix_trie::keys::TrieKey` for the type `_`
src/bin/measurer.rs:19     mask: String,
                           ^~~~~~~~~~~~
src/bin/measurer.rs:16:26: 16:40 note: in this expansion of #[derive_RustcEncodable] (defined in src/bin/measurer.rs)

我的代码也使用了TrieKey来自 radix_tree crate 的特征，它也有一个 encode() 方法。

我希望在范围内同时使用这两个特征，但它们会发生冲突，所以我如何指定 String 的哪个特征用于派生(如果可能的话) ？

不是 useing TrieKey 有效，但我想要一个允许我使用 两者的解决方案。

Answer 1

正如原帖评论下所说，这实际上是bug .现在的修复是 available .