How Does the Tuple Library Improve Your Programs?

• Multiple return values from functions

• Grouping of related types

• Ties values together

C++, like many other programming languages, allows a function to return one value. However, that one value can be of arbitrary type, which allows grouping multiple values as the result, with a struct or class. Although possible, it is often inconvenient to group related return values in such constructs, because it means defining types for every distinct return type needed. To avoid copying large objects in a return value, and to avoid creating a special type to return multiple values from a function, we often resort to using non-const reference arguments or pointers, thereby allowing a function to set the caller's variables through those arguments. This works well in many cases, but some find the output parameters disconcerting in use. Also, output parameters don't emphasize that the return value is in fact return values. Sometimes, std::pair is sufficient, but even that proves insufficient when returning more than two values.

To provide for multiple return values, we need a tuple construct. A tuple is a fixed-size collection of values of specified types. Examples include pairs, triples, quadruples, and so on. Some languages come with such tuple types built in, but C++ doesn't. Given the power inherent in C++, this shortcoming can be amended by a library, which as you no doubt guessed, is just what Boost.Tuple does.

The Tuple library provides tuple constructs that are convenient to use for returning multiple values but also to group any types and operate on them with generic code.