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

Jump to bottom

Mention "extern types" on the opaque structs section #273

Merged
merged 2 commits into from
Jun 18, 2021
Merged

Mention "extern types" on the opaque structs section #273

Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
9387d35
Mention "extern types" on the opaque structs section
JohnTitor Jun 9, 2021
538345a
Turn explanation into a sidenote
JohnTitor Jun 18, 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
11 changes: 8 additions & 3 deletions src/ffi.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -704,9 +704,8 @@ for more information.

# Representing opaque structs

Sometimes, a C library wants to provide a pointer to something, but not let you
know the internal details of the thing it wants. The simplest way is to use a
`void *` argument:
Sometimes, a C library wants to provide a pointer to something, but not let you know the internal details of the thing it wants.
A stable and simple way is to use a `void *` argument:

```c
void foo(void *arg);
Expand Down Expand Up @@ -775,3 +774,9 @@ Notice that it is a really bad idea to use an empty enum as FFI type.
The compiler relies on empty enums being uninhabited, so handling values of type
`&Empty` is a huge footgun and can lead to buggy program behavior (by triggering
undefined behavior).

> **NOTE:** The simplest way would use "extern types".
But it's currently (as of June 2021) unstable and has some unresolved questions, see the [RFC page][extern-type-rfc] and the [tracking issue][extern-type-issue] for more details.

[extern-type-issue]: https://github.com/rust-lang/rust/issues/43467
[extern-type-rfc]: https://rust-lang.github.io/rfcs/1861-extern-types.html