boost::variant. boost::visitor to overloaded function (2 Solutions
Boost.Variant: C++ variant library
COMMENTS
c++
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. typedef boost::variant<int, string, bool> myvar; then you can use myvar directly:
Why doesn't this boost::variant::operator= call compile?
A move assignment operator (which you don't have either) would suffice. As for why a move assignment operator is needed: boost::variant 's operator= is implemented in terms of assignment from another boost::variant. From your int, a boost::variant<int, Foo> is constructed. v is then move-assigned that boost::variant<int, Foo>.
Class template variant
The variant class template (inspired by Andrei Alexandrescu's class of the same name [ Ale01A ]) is an efficient, recursive-capable , bounded discriminated union value type capable of containing any value type (either POD or non-POD). It supports construction from any type convertible to one of its bounded types or from a source variant whose ...
Boost.Variant2: A never valueless variant type
Construction and Assignment If we look at the v.push_back( Circle{ 1.0 } ); line, we can deduce that variant<Rectangle, Circle> can be (implicitly) constructed from Circle (and Rectangle ), and indeed it can. It can also be assigned a Circle or a Rectangle: variant<Rectangle, Circle> v = Circle{ 1.0 }; // v holds Circle v = Rectangle{ 2.0, 3.0 }; // v now holds Rectangle If we try to construct ...
Chapter 43. Boost.Variant
The variant class template is a safe, generic, stack-based discriminated union container, offering a simple solution for manipulating an object from a heterogeneous set of types in a uniform manner. Whereas standard containers such as std::vector may be thought of as " multi-value, single type ," variant is " multi-type, single value ."
Chapter 24. Boost.Variant
This class must overload operator() for every type used by the boost::variant variable it acts on. Consequently, the operator is overloaded three times in Example 24.4 because v supports the types double, char, and std::string.
std::variant<Types...>::operator=
std::variant<Types...>:: operator=. Assigns a new value to an existing variant object. If both *this and rhs are valueless by exception, does nothing. Otherwise, if rhs is valueless, but *this is not, destroys the value contained in *this and makes it valueless. Otherwise, if rhs holds the same alternative as *this, assigns the value contained ...
Tutorial
This macro simplifies for the user the process of declaring variant types in function templates or explicit partial specializations of class templates, as shown in the following: // general cases. template <typename T> void some_func(const T &); template <typename T> class some_class; // function template overload.
Boost users' mailing page: [Boost-users] "Assignment operator could not
I see the warnings with Boost.Variant, Boost.asio and others. My code compiles, and appears to work fine, however, I am always nervous about these kinds of warnings because I suspect there is something waiting to bite me. I guess I am concerned as to what in my code is causing the compiler to want to generate assignment operators.
In reply to: arun.s: "[boost] variant assignment" Hi Arun, Thank you for noting and taking the time to track down this issue! I ... > Im trying to initialize boost variant ( from boost_1_33_1) as below in > MSVC8 > > variant<char* , int> v ; ... > The operator() in statement (3) is never called since T is of const type ( ...
How operator<< with boost::variant is implemented
Boost has an apply_visitor function, that takes a generic function object and passes the type of the variant into it. So implementing operator<< is as straightforward as:
Class template variant
The variant class template (inspired by Andrei Alexandrescu's class of the same name [ Ale01A ]) is an efficient, recursive-capable , bounded discriminated union value type capable of containing any value type (either POD or non-POD). It supports construction from any type convertible to one of its bounded types or from a source variant whose ...
Class template variant
The variant class template (inspired by Andrei Alexandrescu's class of the same name [ Ale01A ]) is an efficient, recursive-capable , bounded discriminated union value type capable of containing any value type (either POD or non-POD). It supports construction from any type convertible to one of its bounded types or from a source variant whose ...
Boost.Variant2: A never valueless variant type
If an attempt to change the contained value (via assignment or emplace ) failed with an exception, and a type with a nonthrowing default constructor existed among the alternatives, a value of that type was created into the variant.
strand::operator=
Converting move assignment operator. ... Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at ...
ip::basic_address_range< address_v4 >::operator=
Boost C++ Libraries...one of the most highly regarded and expertly designed C++ library projects in the world. — Herb Sutter and Andrei Alexandrescu, C++ Coding Standards
windows::basic_random_access_handle::operator= (1 of 2 overloads)
Boost C++ Libraries...one of the most highly regarded and expertly designed C++ library projects in the world. — Herb Sutter and Andrei Alexandrescu, ... This assignment operator moves a random-access handle from one object to another. Parameters. other. The other random-access handle object from which the move will occur. ...
basic_seq_packet_socket::operator= (2 of 2 overloads)
This assignment operator moves a sequenced packet socket from one object to another. Parameters. other. The other basic_seq_packet_socket object from which the move will occur. Remarks. Following the move, the moved ... Distributed under the Boost Software License, Version 1.0.
windows::basic_random_access_handle::operator= (2 of 2 overloads)
Move-assign a random-access handle from a handle of another executor type. template < typename Executor1 > constraint_t < is_convertible < Executor1, Executor >:: value, basic_random_access_handle & > operator =(basic_random_access_handle < Executor1 > && other);. This assignment operator moves a random-access handle from one object to another.
IMAGES
COMMENTS
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. typedef boost::variant<int, string, bool> myvar; then you can use myvar directly:
A move assignment operator (which you don't have either) would suffice. As for why a move assignment operator is needed: boost::variant 's operator= is implemented in terms of assignment from another boost::variant. From your int, a boost::variant<int, Foo> is constructed. v is then move-assigned that boost::variant<int, Foo>.
The variant class template (inspired by Andrei Alexandrescu's class of the same name [ Ale01A ]) is an efficient, recursive-capable , bounded discriminated union value type capable of containing any value type (either POD or non-POD). It supports construction from any type convertible to one of its bounded types or from a source variant whose ...
Construction and Assignment If we look at the v.push_back( Circle{ 1.0 } ); line, we can deduce that variant<Rectangle, Circle> can be (implicitly) constructed from Circle (and Rectangle ), and indeed it can. It can also be assigned a Circle or a Rectangle: variant<Rectangle, Circle> v = Circle{ 1.0 }; // v holds Circle v = Rectangle{ 2.0, 3.0 }; // v now holds Rectangle If we try to construct ...
The variant class template is a safe, generic, stack-based discriminated union container, offering a simple solution for manipulating an object from a heterogeneous set of types in a uniform manner. Whereas standard containers such as std::vector may be thought of as " multi-value, single type ," variant is " multi-type, single value ."
This class must overload operator() for every type used by the boost::variant variable it acts on. Consequently, the operator is overloaded three times in Example 24.4 because v supports the types double, char, and std::string.
std::variant<Types...>:: operator=. Assigns a new value to an existing variant object. If both *this and rhs are valueless by exception, does nothing. Otherwise, if rhs is valueless, but *this is not, destroys the value contained in *this and makes it valueless. Otherwise, if rhs holds the same alternative as *this, assigns the value contained ...
This macro simplifies for the user the process of declaring variant types in function templates or explicit partial specializations of class templates, as shown in the following: // general cases. template <typename T> void some_func(const T &); template <typename T> class some_class; // function template overload.
I see the warnings with Boost.Variant, Boost.asio and others. My code compiles, and appears to work fine, however, I am always nervous about these kinds of warnings because I suspect there is something waiting to bite me. I guess I am concerned as to what in my code is causing the compiler to want to generate assignment operators.
In reply to: arun.s: "[boost] variant assignment" Hi Arun, Thank you for noting and taking the time to track down this issue! I ... > Im trying to initialize boost variant ( from boost_1_33_1) as below in > MSVC8 > > variant<char* , int> v ; ... > The operator() in statement (3) is never called since T is of const type ( ...
Boost has an apply_visitor function, that takes a generic function object and passes the type of the variant into it. So implementing operator<< is as straightforward as:
The variant class template (inspired by Andrei Alexandrescu's class of the same name [ Ale01A ]) is an efficient, recursive-capable , bounded discriminated union value type capable of containing any value type (either POD or non-POD). It supports construction from any type convertible to one of its bounded types or from a source variant whose ...
The variant class template (inspired by Andrei Alexandrescu's class of the same name [ Ale01A ]) is an efficient, recursive-capable , bounded discriminated union value type capable of containing any value type (either POD or non-POD). It supports construction from any type convertible to one of its bounded types or from a source variant whose ...
If an attempt to change the contained value (via assignment or emplace ) failed with an exception, and a type with a nonthrowing default constructor existed among the alternatives, a value of that type was created into the variant.
Converting move assignment operator. ... Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at ...
Boost C++ Libraries...one of the most highly regarded and expertly designed C++ library projects in the world. — Herb Sutter and Andrei Alexandrescu, C++ Coding Standards
Boost C++ Libraries...one of the most highly regarded and expertly designed C++ library projects in the world. — Herb Sutter and Andrei Alexandrescu, ... This assignment operator moves a random-access handle from one object to another. Parameters. other. The other random-access handle object from which the move will occur. ...
This assignment operator moves a sequenced packet socket from one object to another. Parameters. other. The other basic_seq_packet_socket object from which the move will occur. Remarks. Following the move, the moved ... Distributed under the Boost Software License, Version 1.0.
Move-assign a random-access handle from a handle of another executor type. template < typename Executor1 > constraint_t < is_convertible < Executor1, Executor >:: value, basic_random_access_handle & > operator =(basic_random_access_handle < Executor1 > && other);. This assignment operator moves a random-access handle from one object to another.