An implementation of IImmutableDictionary<TKey, TValue> that maintains O(1) value lookup, at the cost of mutation performance.
A good choice when working with dictionaries that remain moderately small and/or that are accessed for reading far more frequently than for modification.
This package also includes an ImmutableHashDictionary static factory class and an ImmutableHashDictionary<TKey, TValue>.Builder class that provide API''s identical to the ImmutableDictionary and ImmutableDictionary<TKey, TValue>.Builder classes.
Targets .NET Standard 2.0.
C#8 (Nullable Reference Types) Compliant.
The following benchmarks demonstrate the performance advantages and disadvantages of the ImmutableHashDictionary<TKey, TValue> class over the Dictionary<TKey, TValue> and ImmutableDictionary<TKey, TValue> classes.
The performance of value lookup by key for ImmutableHashDictionary<TKey, TValue> is, as desired, on par with that of Dictionary<TKey, TValue> and far exceeds that of ImmutableDictionary<TKey, TValue>, even for very large collections.
The performance of single add and remove operations for ImmutableHashDictionary<TKey, TValue> is, as expected, comparable to that of ImmutableDictionary<TKey, TValue> for smaller collections, but does not scale well (O(N) vs O(log N)).
Interestingly, the performance of ranged add and remove operations for ImmutableHashDictionary<TKey, TValue> tends to far exceed that of ImmutableDictionary<TKey, TValue>, and tends to be comparable to that of Dictionary<TKey, TValue> suggesting that the performance costs of mutating an ImmutableHashDictionary can be mitigated by performing mutations in batches, as much as possible.