logo
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26

//! ASN.1 `CHOICE` support.

use crate::{Decodable, Encodable, Tag, Tagged};

/// ASN.1 `CHOICE` denotes a union of one or more possible alternatives.
///
/// The types MUST have distinct tags.
///
/// This crate models choice as a trait, with a blanket impl for all types
/// which impl `Decodable + Encodable + Tagged` (i.e. they are modeled as
/// a `CHOICE` with only one possible variant)
pub trait Choice<'a>: Decodable<'a> + Encodable {
    /// Is the provided [`Tag`] decodable as a variant of this `CHOICE`?
    fn can_decode(tag: Tag) -> bool;
}

/// This blanket impl allows any [`Tagged`] type to function as a [`Choice`]
/// with a single alternative.
impl<'a, T> Choice<'a> for T
where
    T: Decodable<'a> + Encodable + Tagged,
{
    fn can_decode(tag: Tag) -> bool {
        T::TAG == tag
    }
}