Multi-key dictionary in c#? [duplicate]

by

I’ve also used tuples as jason in his answer does. However, I suggest you simply define a tuple as a struct:

public struct Tuple<T1, T2> {
    public readonly T1 Item1;
    public readonly T2 Item2;
    public Tuple(T1 item1, T2 item2) { Item1 = item1; Item2 = item2;} 
}

public static class Tuple { // for type-inference goodness.
    public static Tuple<T1,T2> Create<T1,T2>(T1 item1, T2 item2) { 
        return new Tuple<T1,T2>(item1, item2); 
    }
}

You get immutability, .GetHashcode and .Equals for free, which (while you’re waiting for C# 4.0) is nice ‘n simple…

One warning however: the default GetHashcode implementation (sometimes) only considers the first field so make sure to make the first field the most discriminating or implement GetHashcode yourself (e.g. using FieldwiseHasher.Hash(this) from ValueUtils), otherwise you’ll likely run into scalability issues.

Also, you get to avoid nulls which tend to complicate matters (and if you really want nulls, you just make your Tuple<> nullable). Slightly offtopic, am I the only one annoyed at the framework-level lack of support for non-null references? I work on large project, and occasionally a null creeps in somewhere it really shouldn’t — and hey presto, you get a nullreference exception — but with a stack trace that points you to the reference’s first usage, not the actually faulty code.

Of course, .NET 4.0 is pretty old by now; most of us can just use .NET 4.0’s tuple.

Edit: to workaround the poor GetHashCode implementation that .NET provides for structs I’ve written ValueUtils, which also allows you to use real names for your multi-field keys; that means you might write something like:

sealed class MyValueObject : ValueObject<MyValueObject> {
    public DayOfWeek day;
    public string NamedPart;
    //properties work fine too
}

…which hopefully makes it easier to have human-readable names for data with value semantics, at least until some future version of C# implements proper tuples with named members; hopefully with decent hashcodes ;-).

More Related Contents:

  1. fail to initialize dictionary in c#
  2. How to read lines to dictionary with linQ [closed]
  3. Collection was modified; enumeration operation may not execute
  4. The order of elements in Dictionary
  5. Serialize Class containing Dictionary member
  6. ASP.NET MVC Binding to a dictionary
  7. What is more efficient: Dictionary TryGetValue or ContainsKey+Item?
  8. How to update the value stored in Dictionary in C#?
  9. Hashtable with MultiDimensional Key in C#
  10. Modify Struct variable in a Dictionary
  11. Why doesn’t XmlSerializer support Dictionary?
  12. Proper way to initialize a C# dictionary with values
  13. .NET ObservableDictionary
  14. Convert Dictionary To Anonymous Object?
  15. Multi Value Dictionary?
  16. A dictionary object that uses ranges of values for keys
  17. Enum to Dictionary in C#
  18. Store Dictionary in application settings
  19. Enum to Dictionary in C#
  20. Reverse Sorted Dictionary in .NET
  21. C# dictionary value clearing out when I clear list previously assigned to it….why?
  22. When should I use ConcurrentDictionary and Dictionary?
  23. Good way to get the key of the highest value of a Dictionary in C#
  24. How to sort a dictionary by key
  25. C# Convert List to Dictionary
  26. The given key was not present in the dictionary. Which key?
  27. Best way to change dictionary key
  28. C# anonymous object with properties from dictionary
  29. Get the last element in a dictionary?
  30. Map two lists into a dictionary in C#

Leave a Comment