utils::Box< T > Class Template Reference

#include <userver/utils/box.hpp>

Detailed Description

template<typename T>
class utils::Box< T >

Remote storage for a single item. Implemented as a unique pointer that is never null, except when moved from.

Has the semantics of non-optional T. Copies the content on copy, compares by the contained value.

Use in the following cases:

• to create recursive types while maintaining value semantics;
• to hide the implementation of a class in cpp;
• to prevent the large size or alignment of a field from inflating the size or alignment of an object.

Use utils::UniqueRef instead:

• to add a non-movable field to a movable object;
• to own an object of a polymorphic base class.

Usage example:

struct RecursionStarterPack {
    std::string structs;
    std::string strings;
    utils::Box<PackSection> whats_in_this_section;
};
 
struct PackSection {
    std::string box;
    std::optional<RecursionStarterPack> here_we_go_again;
};
 
TEST(UtilsBox, Sample) {
    PackSection pack{
        "box",
        {{
            "structs",
            "strings",
            utils::Box<PackSection>{{
                "box",
                std::nullopt,
            }},
        }},
    };
 
    // Classic value semantics test.
    auto another_pack = pack;
    EXPECT_EQ(another_pack, pack);
    another_pack.here_we_go_again->structs = "modified structs";
    EXPECT_NE(another_pack, pack);
    EXPECT_EQ(pack.here_we_go_again->structs, "structs");
}

Definition at line 54 of file box.hpp.

Public Member Functions
	Box ()
	Allocate a default-constructed value.
template<typename U = T, std::enable_if_t< impl::ConjunctionWithTrait< impl::kArgsAreNotSelf< Box, U >, std::is_convertible, U &&, T >(), int > = 0>
	Box (U &&arg)
	Allocate a T, copying or moving arg.
template<typename... Args, std::enable_if_t< impl::ConjunctionWithTrait< impl::kArgsAreNotSelf< Box, Args... >, std::is_constructible, T, Args &&... >(), int > = 0>
	Box (Args &&... args)
	Allocate the value, emplacing it with the given args.
	Box (Box &&other) noexcept=default
Box &	operator= (Box &&other) noexcept=default
	Box (const Box &other)
Box &	operator= (const Box &other)
template<typename U = T, std::enable_if_t< impl::ConjunctionWithTrait< impl::ConjunctionWithTrait< impl::kArgsAreNotSelf< Box, U >, std::is_constructible, T, U >(), std::is_assignable, T &, U >(), int > = 0>
Box &	operator= (U &&other)
	Assigns-through to the contained value.
	operator bool () const =delete
T *	operator-> () noexcept
const T *	operator-> () const noexcept
T &	operator* () noexcept
const T &	operator* () const noexcept
bool	operator== (const Box &other) const
bool	operator!= (const Box &other) const
bool	operator< (const Box &other) const
bool	operator> (const Box &other) const
bool	operator<= (const Box &other) const
bool	operator>= (const Box &other) const

Static Public Member Functions
template<typename Factory>
static Box	MakeWithFactory (Factory &&factory)

Constructor & Destructor Documentation

Box() [1/4]

template<typename T>

utils::Box< T >::Box ( )

inline

Allocate a default-constructed value.

Definition at line 59 of file box.hpp.

Box() [2/4]

template<typename T>

template<typename U = T, std::enable_if_t< impl::ConjunctionWithTrait< impl::kArgsAreNotSelf< Box, U >, std::is_convertible, U &&, T >(), int > = 0>

utils::Box< T >::Box ( U && arg )

inline

Allocate a T, copying or moving arg.

Definition at line 76 of file box.hpp.

Box() [3/4]

template<typename T>

template<typename... Args, std::enable_if_t< impl::ConjunctionWithTrait< impl::kArgsAreNotSelf< Box, Args... >, std::is_constructible, T, Args &&... >(), int > = 0>

utils::Box< T >::Box ( Args &&... args )

inlineexplicit

Allocate the value, emplacing it with the given args.

Definition at line 91 of file box.hpp.

Box() [4/4]

template<typename T>

utils::Box< T >::Box ( const Box< T > & other )

inline

Definition at line 103 of file box.hpp.

Member Function Documentation

MakeWithFactory()

template<typename T>

template<typename Factory>

static Box utils::Box< T >::MakeWithFactory ( Factory && factory )

inlinestatic

Allocate the value as constructed by the given factory. Allows to save an extra move of the contained value.

Definition at line 96 of file box.hpp.

operator!=()

template<typename T>

bool utils::Box< T >::operator!= ( const Box< T > & other ) const

inline

Definition at line 147 of file box.hpp.

operator*() [1/2]

template<typename T>

const T & utils::Box< T >::operator* ( ) const

inlinenoexcept

Definition at line 143 of file box.hpp.

operator*() [2/2]

template<typename T>

T & utils::Box< T >::operator* ( )

inlinenoexcept

Definition at line 142 of file box.hpp.

operator->() [1/2]

template<typename T>

const T * utils::Box< T >::operator-> ( ) const

inlinenoexcept

Definition at line 140 of file box.hpp.

operator->() [2/2]

template<typename T>

T * utils::Box< T >::operator-> ( )

inlinenoexcept

Definition at line 139 of file box.hpp.

operator<()

template<typename T>

bool utils::Box< T >::operator< ( const Box< T > & other ) const

inline

Definition at line 149 of file box.hpp.

operator<=()

template<typename T>

bool utils::Box< T >::operator<= ( const Box< T > & other ) const

inline

Definition at line 153 of file box.hpp.

operator=() [1/2]

template<typename T>

Box & utils::Box< T >::operator= ( const Box< T > & other )

inline

Definition at line 105 of file box.hpp.

operator=() [2/2]

template<typename T>

template<typename U = T, std::enable_if_t< impl::ConjunctionWithTrait< impl::ConjunctionWithTrait< impl::kArgsAreNotSelf< Box, U >, std::is_constructible, T, U >(), std::is_assignable, T &, U >(), int > = 0>

Box & utils::Box< T >::operator= ( U && other )

inline

Assigns-through to the contained value.

Definition at line 127 of file box.hpp.

operator==()

template<typename T>

bool utils::Box< T >::operator== ( const Box< T > & other ) const

inline

Definition at line 145 of file box.hpp.

operator>()

template<typename T>

bool utils::Box< T >::operator> ( const Box< T > & other ) const

inline

Definition at line 151 of file box.hpp.

operator>=()

template<typename T>

bool utils::Box< T >::operator>= ( const Box< T > & other ) const

inline

Definition at line 155 of file box.hpp.

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

• userver/utils/box.hpp