Variant< Types > Struct Template Reference

#include <ImFusion/Core/Utils/Variant.h>

Specialization of std::variant offering additional convenience member functions for functionality that the standard library only provides in the form of free functions. More...

Inheritance diagram for Variant< Types >:

Detailed Description

template<typename... Types>
struct ImFusion::Utils::Variant< Types >

Specialization of std::variant offering additional convenience member functions for functionality that the standard library only provides in the form of free functions.

Due to design decisions of the C++ committee interaction with a std::variant requires extensive usage of free functions such as std::get_if<T>() or std::holds_alternative<T>(), which may be disliked for stylistic reasons by some people and also be more difficult to find for people unfamiliar with the interface.

Example:

Utils::Variant<int, std::string, float> var;
if (var.holds<int>())
    std::cout << "variant holds an int\n";
else if (var.equals(42.f))
    std::cout << "variant holds a float with value 42.f\n";
else if (std::string* s = var.getIf<std::string>())
    std::cout << "variant holds the following string: " << *s << '\n';
 
var.visit([](auto&& val) { std::cout << "variant holds: " << val << '\n'; });

Obviously, Utils::Variant behaves exactly like the underlying std::variant and you can still apply the standard library's free functions directly on it.

Note

Prior to C++23 an under-specification of the standard did not require std::visit() to work with classes such as our Utils::Variant. Fortunately, this was fixed with P2162. We tested our implementations for all our target platforms:

• MSVC versions 19.20 (VS 2019) and newer
• GCC's libstdc++ versions 7 and newer
• Clang's libc++ versions 5 and newer

See also

• Utils::Overloaded
• std::variant

Public Member Functions
	Variant (const std::variant< Types... > &rhs)
template<typename T>
constexpr bool	holds () const noexcept
	Checks if the variant holds a value of type T.
template<typename T>
constexpr bool	equals (const T &value) const noexcept
	Checks if the variant holds a value of type T that equals value.
template<typename T>
constexpr T *	getIf () noexcept
	Attempts to retrieve the held value of type T as pointer or returns nullptr otherwise.
template<typename T>
constexpr const T *	getIf () const noexcept
	Attempts to retrieve the held value of type T as pointer or returns nullptr otherwise.
template<class Visitor>
constexpr auto	visit (Visitor &&visitor)
	Applies the set of functions in visitor to this variant, picking the overload matching the current alternative.
template<class Visitor>
constexpr auto	visit (Visitor &&visitor) const
	Applies the set of functions in visitor to this variant, picking the overload matching the current alternative.
Public Member Functions inherited from variant< Types... >
T	emplace (T... args)
T	index (T... args)
T	operator= (T... args)
T	swap (T... args)
T	valueless_by_exception (T... args)
T	variant (T... args)
T	~variant (T... args)

Member Function Documentation

holds()

template<typename... Types>

template<typename T>

bool holds ( ) const

inlineconstexprnoexcept

Checks if the variant holds a value of type T.

T must appear exactly once in Types.

See also

std::holds_alternative()

equals()

template<typename... Types>

template<typename T>

bool equals ( const T & value ) const

inlineconstexprnoexcept

Checks if the variant holds a value of type T that equals value.

This is a convenience function for v.holds<T>() && *v.getIf<T>() == value. T must appear exactly once in Types.

getIf() [1/2]

template<typename... Types>

template<typename T>

T * getIf ( )

inlineconstexprnoexcept

Attempts to retrieve the held value of type T as pointer or returns nullptr otherwise.

T must appear exactly once in Types.

See also

std::get_if<T>()

getIf() [2/2]

template<typename... Types>

template<typename T>

const T * getIf ( ) const

inlineconstexprnoexcept

Attempts to retrieve the held value of type T as pointer or returns nullptr otherwise.

T must appear exactly once in Types.

See also

std::get_if<T>()

visit() [1/2]

template<typename... Types>

template<class Visitor>

auto visit ( Visitor && visitor )

inlineconstexpr

Applies the set of functions in visitor to this variant, picking the overload matching the current alternative.

The visitor must accept every possible Type in Types. Example:

Utils::Variant<int, std::string> var;
var.visit(Utils::Overloaded{
    [](int i) { std::cout << "variant contains an int: "; },
    [](const std::string& s) { "variant contains a string: "; },
});
var.visit([](auto&& value) { std::cout << value << '\n'; });

See also

Utils::Overloaded, std::visit()

visit() [2/2]

template<typename... Types>

template<class Visitor>

auto visit ( Visitor && visitor ) const

inlineconstexpr

Applies the set of functions in visitor to this variant, picking the overload matching the current alternative.

The visitor must accept every possible Type in Types. Example:

Utils::Variant<int, std::string> var;
var.visit(Utils::Overloaded{
    [](int i) { std::cout << "variant contains an int: "; },
    [](const std::string& s) { "variant contains a string: "; },
});
var.visit([](auto&& value) { std::cout << value << '\n'; });

See also

Utils::Overloaded, std::visit()

---

The documentation for this struct was generated from the following file:

• ImFusion/Core/Utils/Variant.h