Better integration between derives and operator overloads · dtolnay/cxx#109

2020-04-11T23:55:44.000Z

Many integration opportunities here. - If a shared struct has a #\[derive(`PartialEq` or `Ord`)\] then emit a compatible `operator ==`, `operator !=`, `operator `, `operator >=` on the type for C++. ```rust mod ffi { #[derive(PartialEq)] struct Key { n: usize, } } ``` - If an opaque Rust type is written with trait bounds then wire up the corresponding operator for C++ in a way that delegates to Rust's implementation of the operator. ```rust mod ffi { extern "Rust" { type R: PartialEq; } } struct R {...} impl PartialEq for R {...} ``` - If an opaque C++ type is written with trait bounds then produce a trait impl in Rust that delegates to the corresponding overloaded operator(s) in C++. ```rust mod ffi { extern "C++" { type C: PartialEq; // produce a PartialEq that calls `operator ==` } } ```

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Description

Many integration opportunities here.

If a shared struct has a #[derive(PartialEq or Ord)] then emit a compatible operator ==, operator !=, operator <, operator <=, operator >, operator >= on the type for C++.
```
mod ffi {
    #[derive(PartialEq)]
    struct Key {
        n: usize,
    }
}
```
If an opaque Rust type is written with trait bounds then wire up the corresponding operator for C++ in a way that delegates to Rust's implementation of the operator.
```
mod ffi {
    extern "Rust" {
        type R: PartialEq;
    }
}

struct R {...}
impl PartialEq for R {...}
```
If an opaque C++ type is written with trait bounds then produce a trait impl in Rust that delegates to the corresponding overloaded operator(s) in C++.
```
mod ffi {
    extern "C++" {
        type C: PartialEq;  // produce a PartialEq that calls `operator ==`
    }
}
```

Contributor guide

Research direction: Implement derive macros that generate C++ operator overloads for structs deriving PartialEq/Ord, and generate trait impls for opaque types binding to C++ operators.
Tech stack: rust
Domain: api
Issue type: Feature
Difficulty: 3
Estimated time: 1-2 days
Activity status: Active
Clarity: Clear
Prerequisites: RustC++
Newbie friendliness: 30

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Description

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