HashBasedSearch 6.0.0

hash-based-search

A small package of extension methods for generic collections to reduce the amount of code required to organize a readonly dictionary lookup by constructing appropriate delegates.

Dictionary is totally readonly since nothing except constructed delegate has access to it.

Supports existing methods of constructing a dictionary based on .ToDictionary overloads. Supports returning a preset default value if the searched element is missing. Supports building search delegate from collection of KeyValuePair's. Supports building search delegate from another Dictionary (by creating new one based on existing).

Benchmarking of some methods presented below. SimpleSearch is implementation of linear search, DictionarySearch~ presents common approach and HashBasedSearch~ presents library usage.

The performance overhead and a few extra bytes allocated are a small price to pay for reducing the amount of code required to perform a dictionary lookup.

Common usage is having some collection, for example:

record Entity(long Id, string Name, int SomeValue);

IEnumerable<Entity> entities;

void TestOne()
{
    HashBasedSearchCallback<long, Entity?> searchEntityCallBack =
        entities.BuildHashBasedSearchCallback(keySelector: entity => entity.Id);
    
    //result is nullable since collection element is nullable and no default value presented
    Entity? searchedEntity = searchEntityCallBack(key: 10);
}

void TestTwo()
{
    HashBasedSearchCallback<long, int?> searchValueCallBack = 
        entities.BuildHashBasedSearchCallbackNullable(
            keySelector: entity => entity.Id,
            elementSelector: entity => entity.SomeValue);
    
    //result is nullable since we use ~Nullable extension on not-nullable resulting element.
    int? searchedValue = searchValueCallBack(key: 10);
    if (searchedValue is null)
    {
        /*do some other work;*/
    }
}

void TestThree()
{
    HashBasedSearchCallback<long, string> searchNameCallBack =
        entities.BuildHashBasedSearchCallback(
            keySelector: entity => entity.Id,
            elementSelector: entity => entity.Name,
            defaultValue: "Name is unknown");
    
    //nullable type result is never null if default value is presented.
    string searchedName = searchNameCallBack(key: 10)!;
    Debug.Assert(searchedName is not null);
}