获取基于哈希的Dictionary或HashTable的值

Question

I have a Dictionary where the keys are objects which are expensive to create. To avoid creating this objects every time I do a search, I have written a function to generate the hash of the object without actually creating it. The problem is, I would like to use the generated hash to search in the Dictionary , but Dictionary doesn't expose such a method ( HashTable doesn't either).

Is it possible to do what I want?

Example

var dict = new Dictionary<ExpensiveObj, int>();
int i = dict.FindValueWithHash(generateHash()); // This is what I am looking for

Answer 1

Use an IEqualityComparer , supplied to the constructor, and use "cheap" algorithm internally to handle a "cheap pseudo-key" as applicable. ¹

Look at the objects supplied - one will be a real object from the Dictionary, the other the "new"/pseudo-key object - to decide how to act. The pseudo-key object will have to conform to the same type as the key to avoid a type error (go interfaces!), but can itself be "cheap to create".

Both the hash code generation and equality must be handled appropriately - otherwise a false-positive (ie. duplication hash) can result.

Or change the algorithm/data-structure so that such an approach is not required.

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¹ If a pseudo-key object always honors pseudo.Equals(real) == real.Equals(pseudo) and pseudo.GetHashCode() == real.GetHashCode() , such that the operations are "cheap" in all cases, then the custom comparer can be skipped as it would then merely bypass correct default behavior.