Macro for implementing Deserialize on simple enums relying on FromStr

impl_deserialize_fromstr.rs

#[macro_export]
macro_rules! impl_deserialize_fromstr {
    ($tyname:ident) => {
        impl ::serde::de::Deserialize for $tyname {
            /// Deserialize this value given this `Deserializer`.
            fn deserialize<D>(deserializer: &mut D) -> ::std::result::Result<Self, D::Error>
                where D: ::serde::de::Deserializer
            {
                struct VariantVisitor<__D> {
                    _marker: ::std::marker::PhantomData<__D>,
                }

                impl<__D> ::serde::de::Visitor for VariantVisitor<__D>
                    where __D: ::serde::de::Deserializer
                {
                    type Value = $tyname;

                    fn visit_str<E>(&mut self, value: &str) -> ::std::result::Result<$tyname, E>
                        where E: ::serde::de::Error
                    {
                        ::std::str::FromStr::from_str(value).map_err(E::invalid_value)
                    }
                }

                deserializer.deserialize_str(VariantVisitor::<D>{
                    _marker: ::std::marker::PhantomData
                })
            }
        }
    }
}