1 unstable release
0.1.0 | Dec 30, 2023 |
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#966 in Rust patterns
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8KB
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enum_downcast
Safe downcasting for enums
Example
#[derive(EnumDowncast)]
enum Enum {
Player(Player),
Enemy(Enemy),
Items { vec: Vec<Item> },
#[enum_downcast(skip)]
Other,
}
let container = Enum::Player(Player { name: "Ryo".to_string() });
let _player_ref: &Player = container.downcast_ref::<Player>().unwrap();
let _player_mut: &mut Player = container.downcast_mut::<Player>().unwrap();
let player: Player = container.downcast::<Player>().unwrap();
You need derive
feature to use the derive macro.
You can see more examples in /examples.
Features
- completely
#![no_std]
- no unsafe code (like
std::mem::transmute
) - no dynamic dispatch
#[enum_downcast(skip)]
to skip some variants (especially not downcastable ones)- enums with type parameters (see example)
- custom downcast implementation without derive macro (see example)
- partial custom downcast implementation for variants with
#[enum_downcast(skip)]
(see example) - compatible with other macros, such as
serde
,strum
, andenum_dispatch
(see example with serde and strum and example with enum_dispatch)
There is one limitation: you cannot compile a code that downcasts an enum to any
type not listed in the enum definition, because of the lack of the
specialization in stable Rust.
You can workaround this by using nightly compiler with min_specialization
feature like
this example.
As of specialization stabilized in the future, this limitation will be cleared,
and you don't need any boilerplate code like the example.
Dependencies
~120KB