Function protobuf::reflect::accessor::make_singular_string_accessor

pub fn make_singular_string_accessor<M: Message + 'static>(name: &'static str,
                                                           has: fn(_: &M) -> bool,
                                                           get: fn<'a>(_: &'a M) -> &'a str)
                                                           -> Box<FieldAccessor + 'static>