How to use flatbuffers `key` attribute to simulate HashMap with flatbuffers in Rust?

I need to create a string to string map with flatbuffers in Rust similar to:

pub struct HashMapIndex {
    keyword_by_filter: HashMap<String, String> // filter text -> keyword
}

I've found some key flatbuffers attribute that can be put on array item, but it seems to be neither documented nor shown in samples:

Can be used for in-place binary search

table KeywordToFilters {
  filter_text: string (key);
  keyword: string;
}

table Index {
  map: [KeywordToFilters];
}

How can i use it (get value by key)? The problem is that no map-like methods are generated - it's just a vector:

pub map: Option<flatbuffers::WIPOffset<flatbuffers::Vector<'a , flatbuffers::ForwardsUOffset<KeywordToFilters<'a >>>>>,

Is there more efficient way to have a map with flatbuffers in Rust?

PS. flatbuffers crate version is 0.8.3