did_doc 0.2.2

Library for loading/saving DID documents.
Documentation 
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use serde::de::{self, MapAccess, SeqAccess, Visitor};
use serde::{Deserialize, Deserializer};
use std::fmt;
use std::marker::PhantomData;
use std::str::FromStr;
use void::Void;

pub fn string_or_list<'de, T, D>(deserializer: D) -> Result<T, D::Error>
where
    T: Deserialize<'de> + FromStr<Err = Void>,
    D: Deserializer<'de>,
{
    // This is a Visitor that wraps string types in a Vec and deserializes Vecs.
    struct StringOrList<T>(PhantomData<fn() -> T>);

    impl<'de, T> Visitor<'de> for StringOrList<T>
    where
        T: Deserialize<'de> + FromStr<Err = Void>,
    {
        type Value = T;

        fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
            formatter.write_str("string or list")
        }

        fn visit_str<E>(self, value: &str) -> Result<T, E>
        where
            E: de::Error,
        {
            Ok(FromStr::from_str(value).unwrap())
        }

        fn visit_seq<S>(self, seq: S) -> Result<T, S::Error>
        where
            S: SeqAccess<'de>,
        {
            // deserialize the sequence
            Deserialize::deserialize(de::value::SeqAccessDeserializer::new(seq))
        }
    }

    deserializer.deserialize_any(StringOrList(PhantomData))
}

// Code lifted verbatim from https://serde.rs/string-or-struct.html
pub fn string_or_struct<'de, T, D>(deserializer: D) -> Result<T, D::Error>
where
    T: Deserialize<'de> + FromStr<Err = Void>,
    D: Deserializer<'de>,
{
    // This is a Visitor that forwards string types to T's `FromStr` impl and
    // forwards map types to T's `Deserialize` impl. The `PhantomData` is to
    // keep the compiler from complaining about T being an unused generic type
    // parameter. We need T in order to know the Value type for the Visitor
    // impl.
    struct StringOrStruct<T>(PhantomData<fn() -> T>);

    impl<'de, T> Visitor<'de> for StringOrStruct<T>
    where
        T: Deserialize<'de> + FromStr<Err = Void>,
    {
        type Value = T;

        fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
            formatter.write_str("string or map")
        }

        fn visit_str<E>(self, value: &str) -> Result<T, E>
        where
            E: de::Error,
        {
            Ok(FromStr::from_str(value).unwrap())
        }

        fn visit_map<M>(self, map: M) -> Result<T, M::Error>
        where
            M: MapAccess<'de>,
        {
            // `MapAccessDeserializer` is a wrapper that turns a `MapAccess`
            // into a `Deserializer`, allowing it to be used as the input to T's
            // `Deserialize` implementation. T then deserializes itself using
            // the entries from the map visitor.
            Deserialize::deserialize(de::value::MapAccessDeserializer::new(map))
        }
    }

    deserializer.deserialize_any(StringOrStruct(PhantomData))
}