原始讨论: https :
似乎与这个旧问题有关: https :
基本上,拥有trait Complete
需要trait Partial
,而trait Partial
需要trait PartialEq
(或任何其他特征),一种类型( struct TypeB
)和impl Complete
不需要满足impl PartialEq
,这看起来只像个错误。
有趣的是,每当看到<TypeB as Partial>
,就会执行检查并抛出适当的错误。
这是一个复制品:
pub trait Partial: PartialEq {
fn foo() -> Option<bool>;
}
pub trait Complete: Partial {
fn foo() -> bool;
}
impl<T> Partial for T
where
T: Complete,
{
fn foo() -> Option<bool> {
Some(<Self as Complete>::foo())
}
}
// ----
#[derive(PartialEq)]
pub struct TypeA {}
impl Partial for TypeA {
fn foo() -> Option<bool> {
None
}
}
// ----
// BUG: No compile warning about `PartialEq` not being implemented
// #[derive(PartialEq)]
pub struct TypeB {}
impl Complete for TypeB {
fn foo() -> bool {
true
}
}
// ----
pub fn main() {
println!("{:?}", TypeA::foo());
// This works, but shouldn't!
println!("{:?}", <TypeB as Complete>::foo());
// This would trigger the issue, though.
//println!("{:?}", <TypeB as Partial>::foo());
/* Result in:
error[E0277]: the trait bound `TypeB: std::cmp::PartialEq` is not satisfied
--> src/bin/cyclic_traits.rs:48:22
|
48 | println!("{:?}", <TypeB as Partial>::foo());
| ^^^^^^^^^^^^^^^^^^^^^^^ can't compare `TypeB` with `TypeB`
|
= help: the trait `std::cmp::PartialEq` is not implemented for `TypeB`
= note: required by `Partial::foo`
*/
}
这是ICE形式的最小化复制:
trait Base {
fn base() {}
}
trait Partial: Base {}
trait Complete: Partial {}
impl<T: Complete> Partial for T {}
struct TypeB;
impl Complete for TypeB {}
fn main() {
ice::<TypeB>();
}
fn ice<P: Partial>() {
P::base();
}
error: internal compiler error: /checkout/src/librustc/traits/trans/mod.rs:75: Encountered error `Unimplemented` selecting `Binder(<TypeB as Base>)` during trans
note: the compiler unexpectedly panicked. this is a bug.
note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports
note: rustc 1.21.0-nightly (cbbe17aa7 2017-08-07) running on x86_64-unknown-linux-gnu
似乎@ arielb1也
我相信这是#43784的重复项,即将结束。
最有用的评论
这是ICE形式的最小化复制: