boost::hana::set< implementation_defined > Struct Template Reference

Description

template<typename implementation_defined>
struct boost::hana::set< implementation_defined >

Basic unordered container requiring unique, Comparable and Hashable keys.

A set is an unordered container that can hold heterogeneous keys. A set requires (and ensures) that no duplicates are present when inserting new keys.

Note

The actual representation of a hana::set is implementation-defined. In particular, one should not take for granted the order of the template parameters and the presence of any additional constructors or assignment operators than what is documented. The canonical way of creating a hana::set is through hana::make_set. More details in the tutorial.

Modeled concepts

1. Comparable
   Two sets are equal iff they contain the same elements, regardless of the order.

   // Copyright Louis Dionne 2013-2017
   // Distributed under the Boost Software License, Version 1.0.
   // (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
    
   #include <boost/hana/assert.hpp>
   #include <boost/hana/equal.hpp>
   #include <boost/hana/integral_constant.hpp>
   #include <boost/hana/not_equal.hpp>
   #include <boost/hana/set.hpp>
   #include <boost/hana/type.hpp>
   namespace hana = boost::hana;
    
    
   int main() {
       BOOST_HANA_CONSTANT_CHECK(
           hana::make_set(hana::int_c<0>, hana::type_c<char>, hana::int_c<1>)
               ==
           hana::make_set(hana::int_c<1>, hana::int_c<0>, hana::type_c<char>)
       );
    
       BOOST_HANA_CONSTANT_CHECK(
           hana::make_set(hana::int_c<0>, hana::type_c<char>)
               !=
           hana::make_set(hana::int_c<1>)
       );
   }

2. Foldable
   Folding a set is equivalent to folding the sequence of its values. However, note that the values are not required to be in any specific order, so using the folds provided here with an operation that is not both commutative and associative will yield non-deterministic behavior.

   // Copyright Louis Dionne 2013-2017
   // Distributed under the Boost Software License, Version 1.0.
   // (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
    
   #include <boost/hana/assert.hpp>
   #include <boost/hana/equal.hpp>
   #include <boost/hana/integral_constant.hpp>
   #include <boost/hana/maximum.hpp>
   #include <boost/hana/minimum.hpp>
   #include <boost/hana/set.hpp>
   #include <boost/hana/sum.hpp>
   namespace hana = boost::hana;
    
    
   int main() {
       constexpr auto xs = hana::make_set(hana::int_c<0>, hana::int_c<1>, hana::int_c<2>);
       static_assert(hana::minimum(xs) == hana::int_c<0>, "");
       static_assert(hana::maximum(xs) == hana::int_c<2>, "");
       static_assert(hana::sum<>(xs) == hana::int_c<3>, "");
   }

3. Searchable
   The elements in a set act as both its keys and its values. Since the elements of a set are unique, searching for an element will return either the only element which is equal to the searched value, or nothing. Also note that operator[] can be used instead of the at_key function.

   // Copyright Louis Dionne 2013-2017
   // Distributed under the Boost Software License, Version 1.0.
   // (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
    
   #include <boost/hana/assert.hpp>
   #include <boost/hana/at_key.hpp>
   #include <boost/hana/equal.hpp>
   #include <boost/hana/find.hpp>
   #include <boost/hana/integral_constant.hpp>
   #include <boost/hana/optional.hpp>
   #include <boost/hana/set.hpp>
   namespace hana = boost::hana;
    
    
   int main() {
       constexpr auto xs = hana::make_set(hana::int_c<0>, hana::int_c<1>, hana::int_c<2>);
       BOOST_HANA_CONSTANT_CHECK(hana::find(xs, hana::int_c<0>) == hana::just(hana::int_c<0>));
       BOOST_HANA_CONSTANT_CHECK(hana::find(xs, hana::int_c<3>) == hana::nothing);
    
       // operator[] is equivalent to at_key
       BOOST_HANA_CONSTANT_CHECK(xs[hana::int_c<2>] == hana::int_c<2>);
    
       // long_c<0> == int_<0>, and therefore int_<0> is found
       BOOST_HANA_CONSTANT_CHECK(xs[hana::long_c<0>] == hana::int_c<0>);
   }

Conversion from any <tt>Foldable</tt>

Any Foldable structure can be converted into a hana::set with to<set_tag>. The elements of the structure must all be compile-time Comparable. If the structure contains duplicate elements, only the first occurence will appear in the resulting set. More specifically, conversion from a Foldable is equivalent to

to<set_tag>(xs) == fold_left(xs, make_set(), insert)

Example

// Copyright Louis Dionne 2013-2017
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
 
#include <boost/hana/assert.hpp>
#include <boost/hana/core/to.hpp>
#include <boost/hana/equal.hpp>
#include <boost/hana/integral_constant.hpp>
#include <boost/hana/set.hpp>
#include <boost/hana/tuple.hpp>
#include <boost/hana/type.hpp>
namespace hana = boost::hana;
 
 
int main() {
    constexpr auto xs = hana::make_tuple(
        hana::int_c<1>,
        hana::int_c<3>,
        hana::type_c<int>,
        hana::long_c<1>
    );
 
    BOOST_HANA_CONSTANT_CHECK(
        hana::to<hana::set_tag>(xs)
            ==
        hana::make_set(hana::int_c<1>, hana::int_c<3>, hana::type_c<int>)
    );
}

Synopsis of associated functions
template<>
constexpr auto	make< set_tag >
	Function object for creating a hana::set. More...
constexpr auto	make_set = make<set_tag>
	Equivalent to make<set_tag>; provided for convenience. More...
constexpr auto	insert
	Insert an element in a hana::set. More...
constexpr auto	erase_key
	Remove an element from a hana::set. More...
constexpr auto	union_
	Returns the union of two sets. More...
constexpr auto	intersection
	Returns the intersection of two sets. More...
constexpr auto	to_set = to<set_tag>
	Equivalent to to<set_tag>; provided for convenience.
constexpr auto	difference
	Returns the set-theoretic difference of two sets. More...
constexpr auto	symmetric_difference
	Returns the symmetric set-theoretic difference of two sets. More...

Friends
template<typename X , typename Y >
constexpr friend auto	operator== (X &&x, Y &&y)
	Equivalent to hana::equal
template<typename X , typename Y >
constexpr friend auto	operator!= (X &&x, Y &&y)
	Equivalent to hana::not_equal

Public Member Functions
constexpr	set ()=default
	Default-construct a set. This constructor only exists when all the elements of the set are default-constructible.
constexpr	set (set const &other)=default
	Copy-construct a set from another set. This constructor only exists when all the elements of the set are copy-constructible.
constexpr	set (set &&other)=default
	Move-construct a set from another set. This constructor only exists when all the elements of the set are move-constructible.
template<typename Key >
constexpr decltype(auto)	operator[] (Key &&key)
	Equivalent to hana::at_key

Associated functions

make< set_tag >

template<typename implementation_defined >

template<>

constexpr auto make< set_tag >

related

Initial value:

= [](auto&& ...xs) {
        return set<implementation_defined>{forwarded(xs)...};
    }

Function object for creating a hana::set.

Given zero or more values xs..., make<set_tag> returns a set containing those values. The values must all be compile-time Comparable, and no duplicate values may be provided. To create a set from a sequence with possible duplicates, use to<set_tag> instead.

Example

// Copyright Louis Dionne 2013-2017
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
 
#include <boost/hana/assert.hpp>
#include <boost/hana/core/make.hpp>
#include <boost/hana/equal.hpp>
#include <boost/hana/integral_constant.hpp>
#include <boost/hana/set.hpp>
#include <boost/hana/type.hpp>
namespace hana = boost::hana;
 
 
constexpr auto xs = hana::make_set(hana::int_c<1>, hana::type_c<void>);
BOOST_HANA_CONSTANT_CHECK(xs == hana::make<hana::set_tag>(hana::int_c<1>, hana::type_c<void>));
 
int main() { }

make_set

template<typename implementation_defined >

constexpr auto make_set = make<set_tag>

related

Equivalent to make<set_tag>; provided for convenience.

Example

// Copyright Louis Dionne 2013-2017
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
 
#include <boost/hana/assert.hpp>
#include <boost/hana/core/make.hpp>
#include <boost/hana/equal.hpp>
#include <boost/hana/integral_constant.hpp>
#include <boost/hana/set.hpp>
#include <boost/hana/type.hpp>
namespace hana = boost::hana;
 
 
constexpr auto xs = hana::make_set(hana::int_c<1>, hana::type_c<void>);
BOOST_HANA_CONSTANT_CHECK(xs == hana::make<hana::set_tag>(hana::int_c<1>, hana::type_c<void>));
 
int main() { }

insert

template<typename implementation_defined >

constexpr auto insert

related

Initial value:

= [](auto&& set, auto&& element) {
        return tag-dispatched;
    }

Insert an element in a hana::set.

If the set already contains an element that compares equal, then nothing is done and the set is returned as is.

Parameters

set	The set in which to insert a value.
element	The value to insert. It must be compile-time Comparable.

Example

// Copyright Louis Dionne 2013-2017
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
 
#include <boost/hana/assert.hpp>
#include <boost/hana/equal.hpp>
#include <boost/hana/insert.hpp>
#include <boost/hana/integral_constant.hpp>
#include <boost/hana/set.hpp>
#include <boost/hana/string.hpp>
#include <boost/hana/type.hpp>
namespace hana = boost::hana;
 
 
int main() {
    constexpr auto xs = hana::make_set(hana::int_c<0>, hana::type_c<int>);
    BOOST_HANA_CONSTANT_CHECK(
        hana::insert(xs, BOOST_HANA_STRING("abc")) ==
        hana::make_set(hana::int_c<0>, hana::type_c<int>, BOOST_HANA_STRING("abc"))
    );
 
    BOOST_HANA_CONSTANT_CHECK(
        hana::insert(xs, hana::int_c<0>) == hana::make_set(hana::int_c<0>, hana::type_c<int>)
    );
}

erase_key

template<typename implementation_defined >

constexpr auto erase_key

related

Initial value:

= [](auto&& set, auto&& element) {
        return tag-dispatched;
    }

Remove an element from a hana::set.

Returns a new set containing all the elements of the original, except the one comparing equal to the given element. If the set does not contain such an element, a new set equal to the original set is returned.

Parameters

set	The set in which to remove a value.
element	The value to remove. It must be compile-time Comparable.

Example

// Copyright Louis Dionne 2013-2017
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
 
#include <boost/hana/assert.hpp>
#include <boost/hana/equal.hpp>
#include <boost/hana/erase_key.hpp>
#include <boost/hana/integral_constant.hpp>
#include <boost/hana/set.hpp>
#include <boost/hana/type.hpp>
namespace hana = boost::hana;
 
 
int main() {
    constexpr auto xs = hana::make_set(hana::int_c<0>, hana::type_c<int>, hana::type_c<void>);
 
    BOOST_HANA_CONSTANT_CHECK(hana::erase_key(xs, hana::type_c<int>) == hana::make_set(hana::int_c<0>, hana::type_c<void>));
    BOOST_HANA_CONSTANT_CHECK(hana::erase_key(xs, hana::type_c<char>) == xs);
}

union_

template<typename implementation_defined >

constexpr auto union_

related

Initial value:

= [](auto&& xs, auto&& ys) {
        return tag-dispatched;
    }

Returns the union of two sets.

Given two sets xs and ys, union_(xs, ys) is a new set containing all the elements of xs and all the elements of ys, without duplicates. For any object x, the following holds: x is in hana::union_(xs, ys) if and only if x is in xs or x is in ys.

Parameters

xs,ys

Two sets to compute the union of.

Example

// Copyright Louis Dionne 2013-2017
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
 
#include <boost/hana/assert.hpp>
#include <boost/hana/equal.hpp>
#include <boost/hana/integral_constant.hpp>
#include <boost/hana/set.hpp>
#include <boost/hana/string.hpp>
#include <boost/hana/type.hpp>
#include <boost/hana/union.hpp>
namespace hana = boost::hana;
using namespace hana::literals;
 
 
constexpr auto xs = hana::make_set(hana::int_c<1>, hana::type_c<void>, hana::int_c<2>);
constexpr auto ys = hana::make_set(hana::int_c<2>, hana::type_c<int>, hana::int_c<3>);
 
BOOST_HANA_CONSTANT_CHECK(hana::union_(xs, ys) == hana::make_set(
    hana::int_c<1>, hana::int_c<2>, hana::int_c<3>, hana::type_c<void>, hana::type_c<int>
));
 
int main() { }

intersection

template<typename implementation_defined >

constexpr auto intersection

related

Initial value:

= [](auto&& xs, auto&& ys) {
        return tag-dispatched;
    }

Returns the intersection of two sets.

Given two sets xs and ys, intersection(xs, ys) is a new set containing exactly those elements that are present both in xs and in ys. In other words, the following holds for any object x:

x ^in^ intersection(xs, ys) if and only if x ^in^ xs && x ^in^ ys

Parameters

xs,ys

Two sets to intersect.

Example

// Copyright Louis Dionne 2013-2017
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
 
#include <boost/hana/assert.hpp>
#include <boost/hana/equal.hpp>
#include <boost/hana/integral_constant.hpp>
#include <boost/hana/intersection.hpp>
#include <boost/hana/set.hpp>
#include <boost/hana/type.hpp>
namespace hana = boost::hana;
 
 
constexpr auto xs = hana::make_set(hana::int_c<1>, hana::type_c<void>, hana::int_c<2>);
constexpr auto ys = hana::make_set(hana::int_c<2>, hana::type_c<int>, hana::int_c<3>);
 
BOOST_HANA_CONSTANT_CHECK(hana::intersection(xs, ys) == hana::make_set(hana::int_c<2>));
 
int main() { }

difference

template<typename implementation_defined >

constexpr auto difference

related

Initial value:

= [](auto&& xs, auto&& ys) {
        return tag-dispatched;
}

Returns the set-theoretic difference of two sets.

Given two sets xs and ys, difference(xs, ys) is a new set containing all the elements of xs that are not contained in ys. For any object x, the following holds:

x ^in^ difference(xs, ys) if and only if x ^in^ xs && !(x ^in^ ys)

This operation is not commutative, i.e. difference(xs, ys) is not necessarily the same as difference(ys, xs). Indeed, consider the case where xs is empty and ys isn't. Then, difference(xs, ys) is empty but difference(ys, xs) is equal to ys. For the symmetric version of this operation, see symmetric_difference.

Parameters

xs	A set param to remove values from.
ys	The set whose values are removed from xs.

Example

// Copyright Louis Dionne 2013-2017
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
 
#include <boost/hana/assert.hpp>
#include <boost/hana/difference.hpp>
#include <boost/hana/equal.hpp>
#include <boost/hana/integral_constant.hpp>
#include <boost/hana/set.hpp>
#include <boost/hana/type.hpp>
namespace hana = boost::hana;
 
 
constexpr auto xs = hana::make_set(hana::int_c<1>, hana::int_c<2>, hana::type_c<int>, hana::int_c<3>);
constexpr auto ys = hana::make_set(hana::int_c<3>, hana::type_c<void>, hana::type_c<int>);
 
BOOST_HANA_CONSTANT_CHECK(hana::difference(xs, ys) == hana::make_set(hana::int_c<1>, hana::int_c<2>));
BOOST_HANA_CONSTANT_CHECK(hana::difference(ys, xs) == hana::make_set(hana::type_c<void>));
 
int main() { }

symmetric_difference

template<typename implementation_defined >

constexpr auto symmetric_difference

related

Initial value:

= [](auto&& xs, auto&& ys) {
        return tag-dispatched;
    }

Returns the symmetric set-theoretic difference of two sets.

Given two sets xs and ys, symmetric_difference(xs, ys) is a new set containing all the elements of xs that are not contained in ys, and all the elements of ys that are not contained in xs. The symmetric difference of two sets satisfies the following:

symmetric_difference(xs, ys) == union_(difference(xs, ys), difference(ys, xs))

Parameters

xs,ys

Two sets to compute the symmetric difference of.

Example

// Copyright Louis Dionne 2013-2017
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
 
#include <boost/hana/assert.hpp>
#include <boost/hana/set.hpp>
#include <boost/hana/symmetric_difference.hpp>
 
namespace hana = boost::hana;
 
 
constexpr auto xs = hana::make_set(hana::int_c<1>, hana::int_c<2>, hana::type_c<int>, hana::int_c<3>);
constexpr auto ys = hana::make_set(hana::int_c<3>, hana::type_c<void>, hana::type_c<int>);
 
BOOST_HANA_CONSTANT_CHECK(
    hana::symmetric_difference(xs, ys) == hana::make_set(hana::int_c<1>, hana::int_c<2>, hana::type_c<void>)
);
 
int main() { }