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Boost.Variant is a powerful C++ library that provides a safe, generic, stack-based discriminated union container. It allows you to manipulate an object from a heterogeneous set of types in a uniform manner. Unlike standard containers like std::vector which are "multi-value, single type," boost::variant is "multi-type, single value"1.
Key Features
Full Value Semantics: Adheres to standard overload resolution rules for conversion operations.
Type-Safe Value Visitation: Compile-time type-safe value visitation via boost::apply_visitor.
Explicit Value Retrieval: Run-time checked explicit value retrieval via boost::get.
Support for Recursive Variant Types: Supports recursive variant types via boost::make_recursive_variant and boost::recursive_wrapper.
Efficient Implementation: Stack-based when possible, ensuring efficient memory usage1.
Basic Usage
To use boost::variant, you need to include the header file and create a variant object with the desired types. Here's a simple example:
c++ - boost::variant usage - Stack Overflow
You can probably use boost::variant with some changes. To start with, you need to tell boost::variant which types it will be storing: boost::variant<int, string, bool> v; Since you probably will be using this type in a few places, you will probably want to create an alias for it. i.e. …
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Chapter 44. Boost.Variant - 1.87.0 - Boost C++ Libraries
Notable features of boost::variant include: Full value semantics, including adherence to standard overload resolution rules for conversion operations. Compile-time type-safe value visitation via …
Chapter 24. Boost.Variant - theboostcpplibraries.com
Boost.Variant provides a class called boost::variant that resembles union. You can store values of different types in a boost::variant variable. At any point only one value can be stored.
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Tutorial - 1.87.0 - Boost C++ Libraries
Any number of bounded types may be specified, up to some implementation-defined limit (see BOOST_VARIANT_LIMIT_TYPES). For example, the following declares a discriminated union …
Boost.Variant2: A never valueless variant type - 1.78.0
Dec 2, 2021 · For example, variant<int64_t, double, std::string> can hold an int64_t value, a double value, or a string value. Such a type is sometimes called a "tagged union", because it’s …
The boost::variant class template addresses these issues in a safe, straightforward, and eficient manner. The following example demonstrates how the class can be used: int operator()(const …
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Boost.Variant (1.87.0)
Boost.Variant, part of collection of the Boost C++ Libraries. It is a safe, generic, stack-based discriminated union container, offering a simple solution for manipulating an object from a …
Chapter 12. Boost.Variant - Brown University
Notable features of boost::variant include: Full value semantics, including adherence to standard overload resolution rules for conversion operations. Compile-time type-safe value visitation via …
Class template variant - 1.87.0 - Boost C++ Libraries
boost::variant — Safe, generic, stack-based discriminated union container. The variant class template (inspired by Andrei Alexandrescu's class of the same name [Ale01A]) is an efficient, …
Tutorial - Brown University
Any number of bounded types may be specified, up to some implementation-defined limit (see BOOST_VARIANT_LIMIT_TYPES). For example, the following declares a discriminated union …
B. Nikolic: Boost.Variant
The Boost.Variant library provides an easy mechanism to write algorithms that process objects that can be one of several types without using object-orientated design and a potentially …
How do boost::variant and boost::any work? - Stack Overflow
Oct 1, 2012 · The key difference between boost::any and boost::variant is that any can store any type, while variant can store only one of a set of enumerated types. The any type stores a …
How to use Boost Variant with struct objects C++
Apr 10, 2017 · As for your problem, use boost::get to get a reference to the specific structure. (See the Boost variant tutorial for an example on how to use it) The variant type doesn't have the …
boost::variant and a general, generic visitor class - Meetingcpp
Jul 25, 2015 · With boost::variant, you simply derive your visitor class from the static_visitor class, which lets you visit the types in a boost::variant via the call operator. When you want to do …
Boost.Variant2: A never valueless variant type - 1.71.0
Aug 14, 2019 · Variants can be used to represent dynamically-typed values. A configuration file of the form. std::string>>. Variants can also represent polymorphism. To take a classic example, …
Boost.Variant (develop)
Boost.Variant, part of collection of the Boost C++ Libraries. It is a safe, generic, stack-based discriminated union container, offering a simple solution for manipulating an object from a …
Reference - 1.87.0 - Boost C++ Libraries
Provides forward declarations of the boost::variant, boost::make_variant_over, boost::make_recursive_variant, and boost::make_recursive_variant_over class templates and …
What is boost::variant memory and performance cost?
Oct 2, 2014 · The size of boost::variant is is the max size of any element, rounded up as needed for the largest alignment, plus the size of some integer, and again rounded up. Think about a …
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