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c61a0092bc
This is a [breaking-change]. The new rules require that, for an impl of a trait defined
in some other crate, two conditions must hold:
1. Some type must be local.
2. Every type parameter must appear "under" some local type.
Here are some examples that are legal:
```rust
struct MyStruct<T> { ... }
// Here `T` appears "under' `MyStruct`.
impl<T> Clone for MyStruct<T> { }
// Here `T` appears "under' `MyStruct` as well. Note that it also appears
// elsewhere.
impl<T> Iterator<T> for MyStruct<T> { }
```
Here is an illegal example:
```rust
// Here `U` does not appear "under" `MyStruct` or any other local type.
// We call `U` "uncovered".
impl<T,U> Iterator<U> for MyStruct<T> { }
```
There are a couple of ways to rewrite this last example so that it is
legal:
1. In some cases, the uncovered type parameter (here, `U`) should be converted
into an associated type. This is however a non-local change that requires access
to the original trait. Also, associated types are not fully baked.
2. Add `U` as a type parameter of `MyStruct`:
```rust
struct MyStruct<T,U> { ... }
impl<T,U> Iterator<U> for MyStruct<T,U> { }
```
3. Create a newtype wrapper for `U`
```rust
impl<T,U> Iterator<Wrapper<U>> for MyStruct<T,U> { }
```
Because associated types are not fully baked, which in the case of the
`Hash` trait makes adhering to this rule impossible, you can
temporarily disable this rule in your crate by using
`#![feature(old_orphan_check)]`. Note that the `old_orphan_check`
feature will be removed before 1.0 is released.
108 lines
2.4 KiB
Rust
108 lines
2.4 KiB
Rust
// Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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//! The Rust parser and macro expander.
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//!
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//! # Note
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//!
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//! This API is completely unstable and subject to change.
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#![crate_name = "syntax"]
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#![experimental]
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#![crate_type = "dylib"]
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#![crate_type = "rlib"]
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#![doc(html_logo_url = "http://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
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html_favicon_url = "http://www.rust-lang.org/favicon.ico",
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html_root_url = "http://doc.rust-lang.org/nightly/")]
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#![allow(unknown_features)]
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#![feature(macro_rules, globs, default_type_params, phase, slicing_syntax)]
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#![feature(quote, unsafe_destructor)]
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#![feature(unboxed_closures)]
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#![feature(old_orphan_check)]
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extern crate arena;
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extern crate fmt_macros;
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#[phase(plugin, link)] extern crate log;
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extern crate serialize;
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extern crate term;
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extern crate libc;
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extern crate "serialize" as rustc_serialize; // used by deriving
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pub mod util {
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pub mod interner;
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#[cfg(test)]
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pub mod parser_testing;
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pub mod small_vector;
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}
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pub mod diagnostics {
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pub mod macros;
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pub mod plugin;
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pub mod registry;
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}
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pub mod syntax {
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pub use ext;
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pub use parse;
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pub use ast;
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}
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pub mod abi;
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pub mod ast;
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pub mod ast_map;
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pub mod ast_util;
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pub mod attr;
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pub mod codemap;
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pub mod config;
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pub mod diagnostic;
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pub mod feature_gate;
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pub mod fold;
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pub mod owned_slice;
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pub mod parse;
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pub mod ptr;
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pub mod show_span;
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pub mod std_inject;
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pub mod test;
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pub mod visit;
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pub mod print {
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pub mod pp;
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pub mod pprust;
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}
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pub mod ext {
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pub mod asm;
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pub mod base;
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pub mod build;
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pub mod bytes;
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pub mod cfg;
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pub mod cfg_attr;
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pub mod concat;
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pub mod concat_idents;
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pub mod deriving;
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pub mod env;
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pub mod expand;
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pub mod fmt;
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pub mod format;
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pub mod log_syntax;
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pub mod mtwt;
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pub mod quote;
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pub mod source_util;
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pub mod trace_macros;
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pub mod tt {
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pub mod transcribe;
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pub mod macro_parser;
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pub mod macro_rules;
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}
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}
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