What requirement was the tuple designed to solve?

Solution 1:

When writing programs it is extremely common to want to logically group together a set of values which do not have sufficient commonality to justify making a class.

Many programming languages allow you to logically group together a set of otherwise unrelated values without creating a type in only one way:

void M(int foo, string bar, double blah)

Logically this is exactly the same as a method M that takes one argument which is a 3-tuple of int, string, double. But I hope you would not actually make:

class MArguments
{
   public int Foo { get; private set; } 
   ... etc

unless MArguments had some other meaning in the business logic.

The concept of "group together a bunch of otherwise unrelated data in some structure that is more lightweight than a class" is useful in many, many places, not just for formal parameter lists of methods. It's useful when a method has two things to return, or when you want to key a dictionary off of two data rather than one, and so on.

Languages like F# which support tuple types natively provide a great deal of flexibility to their users; they are an extremely useful set of data types. The BCL team decided to work with the F# team to standardize on one tuple type for the framework so that every language could benefit from them.

However, there is at this point no language support for tuples in C#. Tuples are just another data type like any other framework class; there's nothing special about them. We are considering adding better support for tuples in hypothetical future versions of C#. If anyone has any thoughts on what sort of features involving tuples you'd like to see, I'd be happy to pass them along to the design team. Realistic scenarios are more convincing than theoretical musings.

Solution 2:

Tuples provide an immutable implementation of a collection

Aside from the common uses of tuples:

to group common values together without having to create a class
to return multiple values from a function/method
etc...

Immutable objects are inherently thread safe:

Immutable objects can be useful in multi-threaded applications. Multiple threads can act on data represented by immutable objects without concern of the data being changed by other threads. Immutable objects are therefore considered to be more thread-safe than mutable objects.

From "Immutable Object" on wikipedia

Solution 3:

It provides an alternative to ref or out if you have a method that needs to return multiple new objects as part of its response.

It also allows you to use a built-in type as a return type if all you need to do is mash-up two or three existing types, and you don't want to have to add a class/struct just for this combination. (Ever wish a function could return an anonymous type? This is a partial answer to that situation.)

Solution 4:

It's often helpful to have a "pair" type, just used in quick situations (like returning two values from a method). Tuples are a central part of functional languages like F#, and C# picked them up along the way.

Solution 5:

very useful for returning two values from a function