Call a C++ method which is only safe Rust for some pointer types

[teor2345]

An interop API has the following properties:

• a C++ method is safe to call in Rust on some pointer/reference types, but unsafe on others
• the Rust methods should have the same name, because the underlying C++ method is the same
• in Rust, the unsafe method will be called in an unsafe block, so using a suffixed name is redundant:

unsafe { MyCppType::do_the_thing_unsafe(…) }

Example Code

This can be supported using inherent trait impls and trait-based Rust method name overloading. This allows writing the same method name with two different receiver types, one safe and one unsafe:

pub struct MyCppType;

impl MyCppType {
    fn do_the_thing(&mut self) { ... }
}

trait MyCppTypeUnsafe {
    unsafe fn do_the_thing(self: CMut<'_, Self>);
}

#[inherent]
impl MyCppTypeUnsafe for MyCppType { ... }

Calls look like:

unsafe { MyCppTypeUnsafe::do_the_thing(...) }
MyCppType::do_the_thing(...)
<MyCppType as Self>::do_the_thing(...)

Rust Compiler Features

• inherent trait impls

Sources

• https://rust-lang.zulipchat.com/#narrow/channel/213817-t-lang/topic/On.20overloading/near/581005466