Professional C++, 5th Edition

24Additional Library Utilities

WHAT'S IN THIS CHAPTER?

• How to use the variant and any data types
• What tuples are and how to use them

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This chapter discusses some additional library functionality provided by the C++ Standard Library that's worth looking at. It starts the discussion with two more vocabulary types, variant and any, that complement the optional vocabulary type discussed in Chapter 1, “A Crash Course in C++ and the Standard Library.” The chapter finishes with a discussion of tuple s, a generalization of pair s.

VOCABULARY TYPES

This section examines the vocabulary types variant and any.

variant

std::variant, defined in <variant>, can hold a single value of one of a given set of types. When you define a variant, you have to specify the types it can potentially contain. For example, the following code defines a variant that can contain an integer, a string, or a floating-point value, one at a time:

variant<int, string, float> v;

The template type arguments for a variant must be unique; for example, variant<int,int> is invalid. A default-constructed variant contains a default-constructed value of its first type, int in the case of the variant v. If you want to be able to default construct a variant, you have to make sure that ...