Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Clarify object safety rules for methods striked from the vtable #965

Merged
merged 2 commits into from
Apr 1, 2021
Merged

Clarify object safety rules for methods striked from the vtable #965

Changes from 1 commit
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
bab2c58
Clarify object safety rules for methods striked from the vtable
guswynn Feb 18, 2021
1151724
comments
guswynn Mar 31, 2021
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
33 changes: 17 additions & 16 deletions src/items/traits.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -67,23 +67,23 @@ trait Seq<T> {
Object safe traits can be the base trait of a [trait object]. A trait is
*object safe* if it has the following qualities (defined in [RFC 255]):

* It must not require `Self: Sized`
* All associated functions must either have a `where Self: Sized` bound, or
* Not have any type parameters (although lifetime parameters are allowed),
and
* Be a [method] that does not use `Self` except in the type of the receiver.
* All [supertraits] must also be object safe.
* It must not require `Self: Sized` (i.e. `Sized` must not be a [supertrait][supertraits])
Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Suggested change
* It must not require `Self: Sized` (i.e. `Sized` must not be a [supertrait][supertraits])
* `Sized` must not be a [supertrait][supertraits]. In other words, it must not require `Self: Sized`.

Let's avoid the latinisms like "i.e."

* It must not have any associated constants.
* All supertraits must also be object safe.

When there isn't a `Self: Sized` bound on a method, the type of a method
receiver must be one of the following types:

* `&Self`
* `&mut Self`
* [`Box<Self>`]
* [`Rc<Self>`]
* [`Arc<Self>`]
* [`Pin<P>`] where `P` is one of the types above
* All associated functions must "dispatchable from a trait object" or "explicitly non-dispatchable from a trait object":
Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Suggested change
* All associated functions must "dispatchable from a trait object" or "explicitly non-dispatchable from a trait object":
* All associated functions must either be dispatchable from a trait object or be explicitly non-dispatchable:

* Dispatchable functions require:
* Not have any type parameters (although lifetime parameters are allowed),
* Be a [method] that does not use `Self` except in the type of the receiver.
* Have a receiver with one of the following types:
* `&Self` (i.e. `&self`)
* `&mut Self` (i.e `&mut self`)
* [`Box<Self>`]
* [`Rc<Self>`]
* [`Arc<Self>`]
* [`Pin<P>`] where `P` is one of the types above
* Does not have a `where Self: Sized` bound (reciever type of `Self` (i.e. `self`) implies this).
* Explicitly non-dispatchable functions require:
* Have a `where Self: Sized` bound (reciever type of `Self` (i.e. `self`) implies this).

```rust
# use std::rc::Rc;
Expand Down Expand Up @@ -325,6 +325,7 @@ fn main() {
[RFC 255]: https://github.com/rust-lang/rfcs/blob/master/text/0255-object-safety.md
[associated items]: associated-items.md
[method]: associated-items.md#methods
[supertraits]: #supertraits
[implementations]: implementations.md
[generics]: generics.md
[where clauses]: generics.md#where-clauses
Expand Down