Have you ever?:

• used KeyValuePair{TKey,TValue} just to hold a pair of values together
• missed the fact that .NET anonymous types can be passed out of the method
• used multiple out references to pass parameters out of the function
• wished that Microsoft has declared Triplet somewhere in the System.

The answer to these problems is a tuple. It is an ordered list of items of some specific length. KeyValuePair, for example, is n-tuple of length 2.

Simply put, tuple is just a piece of data that holds a couple of objects together and does not have any other special meaning or usage.

Tuple classes are normally named like:

• 2 arguments - Pair
• 3 items - Triple
• 4 items - Quad or Quadruple

Sample implementation for these classes (with the proper DebuggerDisplay, ToString(), hashcode and equality routines) could be found in the Lokad Shared codebase).

Variable Composition

Sample usage is trivial. Although, it is more clumsy, than in F#, but that's still convenient in some cases, when writing a new class just for one usage is not feasible:

Tuple<bool,DataTable> SomeTupleFunction()
{
  bool thereAreMoreRecords = false;
  DataTable table;
  // ...
  return Tuple.From(thereAreMoreRecords, table);
}

// ...

var t = SomeTupleFunction();
var moreRecords = t.Item1;
var table = t.Item2;

Btw, I've recently seen such over-usage of KeyValuePair:

KeyValuePair<string,KeyValuePair<int,KeyValuePair<...

Representing Keys

Another important feature of tuples is their ability to represent keys in dictionaries and hashsets

Consider the following example:

var set = new HashSet<Triple<int, bool, bool>>
  {
    Tuple.From(1, true, false),
    Tuple.From(1, true, true)
  };

Assert.IsTrue(set.Contains(Tuple.From(1,true,false)));
Assert.IsFalse(set.Contains(Tuple.From(2, true, true)));

As you can see, generic tuple implementation, saves us the effort to create our own classes with GetHashCode and Equals overrides.

Please, check out the library for yourself and tell me what you think about this implementation of tuples. How could it be improved?