trait-union

This crate provides a macro that generates a trait-union type. That is, a trait object type which can contain any one of a pre-determined set of implementors.

The generated type does not allocate. The size of the type is the size of the largest variant plus some constant overhead.

NOTE: As of rustc 1.47, you must enable the untagged_unions feature to store non-Copy types in a trait-union. This will change soon.

Example

 use trait_union::trait_union;
 use std::fmt::Display;

trait_union! {
    /// Container can contain either an i32, a &'static str, or a bool.
    union Container: Display = i32 | &'static str | bool;
}

let mut container = Container::new(32);
assert_eq!(container.to_string(), "32");

container = Container::new("Hello World");
assert_eq!(container.to_string(), "Hello World");

container = Container::new(true);
assert_eq!(container.to_string(), "true");

License

This project is licensed under either of

• Apache License, Version 2.0
• MIT License

at your option.