Macro asn1_choice

macro_rules! asn1_choice {
    (
        choice $name:ident {
            $( $variant:ident($combinator:expr): $combinator_type:ty ),+
            $(,)?
        }
    ) => { ... };
}

Generate a combinator for an ASN.1 CHOICE

For example

asn1_choice! {
    choice Test {
        PrintableString(ASN1(PrintableString)): ASN1<PrintableString>,
        UTF8String(ASN1(UTF8String)): ASN1<UTF8String>,
    }
}

This essentially generates an OrdChoice combinator over all the choices

NOTE: Since we can’t generate match branches in macros, there is a small artifact in the definition of the result type: a last variant with name Unreachable, which should never be produced at runtime as the combinator of Unreachable always fails