Boost.MultiIndex Key extraction reference

Sequenced indices

Boost.MultiIndex reference

Compiler specifics

Contents

• Key Extractors
  • Chained pointers
• Header "boost/multi_index/key_extractors.hpp" synopsis
• Header "boost/multi_index/identity.hpp" synopsis
  • Class template identity
• Header "boost/multi_index/member.hpp" synopsis
  • Class template member
  • Class template member_offset
  • Macro BOOST_MULTI_INDEX_MEMBER
• Header "boost/multi_index/mem_fun.hpp" synopsis
  • Class template const_mem_fun
  • Class template mem_fun
  • Class template const_mem_fun_explicit
  • Class template mem_fun_explicit
  • Macro BOOST_MULTI_INDEX_CONST_MEM_FUN
  • Macro BOOST_MULTI_INDEX_MEM_FUN
• Header "boost/multi_index/composite_key.hpp" synopsis
  • Class template composite_key
  • Class template composite_key_result
  • Equality
    • Class template composite_key_equal_to
    • Class template composite_key_result_equal_to
    • Specialization of std::equal_to for composite_key results
  • Comparison
    • Class template composite_key_compare
    • Class template composite_key_result_less
    • Class template composite_key_result_greater
    • Specialization of std::less for composite_key results
    • Specialization of std::greater for composite_key results
  • Hashing
    • Class template composite_key_hash
    • Class template composite_key_result_hash
    • Specialization of boost::hash for composite_key results
  • Semantics of composite_key_result

Key Extractors

Key extraction classes are used by key-based indices to obtain the indexing keys from the elements of a multi_index_container. An Assignable class KeyFromValue is said to be a key extractor from a type Type if

1. the type KeyFromValue::result_type is defined,
2. k1(ca) is defined and returns a value convertible to const KeyFromValue::result_type&,
3. if k2 is a copy of k1, k1(ca) is the same value as k2(ca),

Additionally, KeyFromValue is a read/write key extractor if the following extra conditions are met:

1. k1(a) is defined and returns a value convertible to KeyFromValue::result_type&,
2. const_cast<const KeyFromValue::result_type&>(k1(a)) is the same value as k1(const_cast<const Type&>(a)),

Boost.MultiIndex provides five general-purpose key extractors:

• identity,
• member,
• const_mem_fun,
• mem_fun and
• composite_key,

• member_offset,
• const_mem_fun_explicit and
• mem_fun_explicit,

Chained pointers

The key extractors provided by Boost.MultiIndex are templatized according to the type Type and serve to extract keys not only from objects of type Type, but also from reference wrappers provided by Boost.Ref and from chained pointers to Type (or to reference wrappers of Type): a chained pointer is any type P such that, for an object p of type const P

• *p yields an object of type Type& or boost::reference_wrapper<Type>, OR
• *p yields a chained pointer to Type,

Header "boost/multi_index/key_extractors.hpp" synopsis

#include <boost/multi_index/identity.hpp>
#include <boost/multi_index/member.hpp>
#include <boost/multi_index/mem_fun.hpp>
#include <boost/multi_index/composite_key.hpp>

This header includes all the key extractors provided by Boost.MultiIndex.

Header "boost/multi_index/identity.hpp" synopsis

namespace boost{

namespace multi_index{

template<typename T> struct identity;

} // namespace boost::multi_index 

} // namespace boost

Class template identity

identity is a Key Extractor that acts as a do-nothing identity functor.

template<typename Type>
struct identity
{
  typedef Type result_type;

  template<typename ChainedPtr> Type& operator()(const ChainedPtr& x)const;
  const Type& operator()(const Type& x)const; 
  Type&       operator()(Type& x)const; // only provided if Type is non-const

  // only provided if Type is non-const
  const Type& operator()(const reference_wrapper<const Type>& x)const; 

  // only provided if Type is const
  Type& operator()(
    const reference_wrapper<typename remove_const<Type>::type>& x)const; 

  Type& operator()(const reference_wrapper<Type>& x)const;
};

identity<Type> is a model of:

• read/write Key Extractor from Type,
• Key Extractor from reference_wrapper<const Type>,
• read/write Key Extractor from reference_wrapper<Type>,
• Key Extractor from any chained pointer to const Type,
• read/write Key Extractor from any chained pointer to Type.

identity members

Requires: ChainedPtr is a chained pointer type to Type.
Returns: a reference to the object chained-pointed to by x.

Returns: x.

Returns: x.

Returns: x.get().

Returns: x.get().

Returns: x.get().

Header "boost/multi_index/member.hpp" synopsis

namespace boost{

namespace multi_index{

template<class Class,typename Type,Type Class::*PtrToMember>
struct member;

template<class Class,typename Type,std::size_t OffsetOfMember>
struct member_offset;

#define BOOST_MULTI_INDEX_MEMBER(Class,Type,MemberName) implementation defined

} // namespace boost::multi_index 

} // namespace boost

Class template member

member is a Key Extractor aimed at accessing a given member of a class.

template<class Class,typename Type,Type Class::*PtrToMember>
struct member
{
  typedef Type result_type;

  template<typename ChainedPtr> Type& operator()(const ChainedPtr& x)const;
  const Type& operator()(const Class& x)const;
  Type&       operator()(Class& x)const; // only provided if Type is non-const
  const Type& operator()(const reference_wrapper<const Class>& x)const;
  Type&       operator()(const reference_wrapper<Class>& x)const;
};

The PtrToMember template argument specifies the particular Type Class::* pointer to the member to be extracted. member<Class,Type,PtrToMember> is a model of:

• read/write Key Extractor from Class,
• Key Extractor from reference_wrapper<const Class>,
• read/write Key Extractor from reference_wrapper<Class>,
• Key Extractor from any chained pointer to const Class,
• read/write Key Extractor from any chained pointer to Class.

member members

Requires: ChainedPtr is a chained pointer type to Type.
Returns: a reference to the object chained-pointed to by x.

Returns: x.*PtrToMember.

Returns: x.*PtrToMember.

Returns: x.get().*PtrToMember.

Returns: x.get().*PtrToMember.

Class template member_offset

Some compilers do not properly support pointers to members as non-type template arguments. The following have been confirmed to have bugs in this respect:

• MSVC++ 6.0 (see Microsoft Knowledge Base article #249045),
• MSVC++ 7.0 (not officially confirmed by Microsoft),
• Intel C++ 7.0/7.1 for Windows (support issue #207321),
• VisualAge 6.0 for AIX (internal defect #288539.)

template<class Class,typename Type,std::size_t OffsetOfMember>
struct member_offset
{
  typedef Type result_type;

  template<typename ChainedPtr> Type& operator()(const ChainedPtr& x)const;
  const Type& operator()(const Class& x)const; 
  Type&       operator()(Class& x)const; // only provided if Type is non-const
  const Type& operator()(const reference_wrapper<const Class>& x)const;
  Type&       operator()(const reference_wrapper<Class>& x)const;
};

As an example of use, given the class

class A
{
  int x;
}

the instantiation member<A,int,&A::x> can be simulated then as member_offset<A,int,offsetof(A,x)>.

Macro BOOST_MULTI_INDEX_MEMBER

BOOST_MULTI_INDEX_MEMBER(Class,Type,MemberName)

This macro is provided as an aid for using member and member_offset when writing cross-platform code. In the usual cases, it expands to

::boost::multi_index::member<Class,Type,&Class::MemberName>

but it resolves to

::boost::multi_index::member_offset<Class,Type,offsetof(Class,MemberName)>

if the Boost Configuration Library defect macro BOOST_NO_POINTER_TO_MEMBER_TEMPLATE_PARAMETERS is defined.

Header "boost/multi_index/mem_fun.hpp" synopsis

namespace boost{

namespace multi_index{

template<class Class,typename Type,Type (Class::*PtrToMemberFunction)()const>
struct const_mem_fun;

template<class Class,typename Type,Type (Class::*PtrToMemberFunction)()>
struct mem_fun;

template<
  class Class,typename Type,
  typename PtrToMemberFunctionType,PtrToMemberFunctionType PtrToMemberFunction
>
struct const_mem_fun_explicit;

template<
  class Class,typename Type,
  typename PtrToMemberFunctionType,PtrToMemberFunctionType PtrToMemberFunction
>
struct mem_fun_explicit;

#define BOOST_MULTI_INDEX_CONST_MEM_FUN(Class,Type,MemberFunName) \
implementation defined
#define BOOST_MULTI_INDEX_MEM_FUN(Class,Type,MemberFunName) \
implementation defined

} // namespace boost::multi_index 

} // namespace boost

Class template const_mem_fun

const_mem_fun is a Key Extractor returning as key the result of invoking a given constant member function of a class.

template<class Class,typename Type,Type (Class::*PtrToMemberFunction)()const>
struct const_mem_fun
{
  typedef typename remove_reference<Type>::type result_type;

  template<typename ChainedPtr> Type operator()(const ChainedPtr& x)const;
  Type operator()(const Class& x)const;
  Type operator()(const reference_wrapper<const Class>& x)const;
  Type operator()(const reference_wrapper<Class>& x)const;
};

The PtrToMemberFunction template argument specifies the particular Type (Class::*PtrToMemberFunction)()const pointer to the the constant member function used in the extraction. const_mem_fun<Class,Type,PtrToMemberFunction> is a model of:

• Key Extractor from Class,
• Key Extractor from reference_wrapper<const Class>,
• Key Extractor from reference_wrapper<Class>,
• Key Extractor from any chained pointer to const Class,
• Key Extractor from any chained pointer to Class.

const_mem_fun members

Requires: ChainedPtr is a chained pointer type to Type.
Returns: (y.*PtrToMemberFunction)(), where y is the object chained-pointed to by x.

Returns: (x.*PtrToMemberFunction)().

Returns: (x.get().*PtrToMemberFunction)().

Returns: (x.get().*PtrToMemberFunction)().

Class template mem_fun

mem_fun is a Key Extractor returning as key the result of invoking a given member function of a class.

template<class Class,typename Type,Type (Class::*PtrToMemberFunction)()>
struct mem_fun
{
  typedef typename remove_reference<Type>::type result_type;

  template<typename ChainedPtr> Type operator()(const ChainedPtr& x)const;
  Type operator()(Class& x)const;
  Type operator()(const reference_wrapper<Class>& x)const;
};

The PtrToMemberFunction template argument specifies the particular Type (Class::*PtrToMemberFunction)() pointer to the the member function used in the extraction. mem_fun<Class,Type,PtrToMemberFunction> is a model of:

• Key Extractor from reference_wrapper<Class>,
• Key Extractor from any chained pointer to Class.

mem_fun members

Requires: ChainedPtr is a chained pointer type to Type.
Returns: (y.*PtrToMemberFunction)(), where y is the object chained-pointed to by x.

Returns: (x.*PtrToMemberFunction)().

Returns: (x.get().*PtrToMemberFunction)().

Class template const_mem_fun_explicit

MSVC++ 6.0 do not properly support pointers to constant member functions as non-type template parameters, thus const_mem_fun cannot be used in this compiler. A simple workaround consists in specifying the type of these pointers as an additional template parameter.

template<
  class Class,typename Type,
  typename PtrToMemberFunctionType,PtrToMemberFunctionType PtrToMemberFunction
>
struct const_mem_fun_explicit
{
  typedef typename remove_reference<Type>::type result_type;

  template<typename ChainedPtr> Type operator()(const ChainedPtr& x)const;
  Type operator()(const Class& x)const;
  Type operator()(const reference_wrapper<const Class>& x)const;
  Type operator()(const reference_wrapper<Class>& x)const;
};

const_mem_fun_explicit provides the very same functionality as its const_mem_fun analogous instantiation. For example, given the type

struct A
{
  int f()const;
};

the extractor const_mem_fun<A,int,&A::f> can be replaced by const_mem_fun_explicit<A,int,int (A::*)()const,&A::f>.

Class template mem_fun_explicit

For analogy with const_mem_fun_explicit, a variation of mem_fun is provided accepting an additional parameter with the type of the pointer to non-constant member function used for extraction.

template<
  class Class,typename Type,
  typename PtrToMemberFunctionType,PtrToMemberFunctionType PtrToMemberFunction
>
struct mem_fun_explicit
{
  typedef typename remove_reference<Type>::type result_type;

  template<typename ChainedPtr> Type operator()(const ChainedPtr& x)const;
  Type operator()(Class& x)const;
  Type operator()(const reference_wrapper<Class>& x)const;
};

Macro BOOST_MULTI_INDEX_CONST_MEM_FUN

BOOST_MULTI_INDEX_CONST_MEM_FUN(Class,Type,MemberFunName)

Use this macro when writing cross-platform code selectively using const_mem_fun_explicit in place of const_mem_fun for compilers not supporting the latter. In the usual cases, the macro expands to

::boost::multi_index::const_mem_fun<Class,Type,&Class::MemberFunName>

but it resolves to

::boost::multi_index::const_mem_fun_explicit<
  Class,Type,Type (Class::*)()const,&Class::MemberFunName
>

for MSVC++ 6.0 or lower.

Macro BOOST_MULTI_INDEX_MEM_FUN

BOOST_MULTI_INDEX_MEM_FUN(Class,Type,MemberFunName)

By default, the macro expands to

::boost::multi_index::mem_fun<Class,Type,&Class::MemberFunName>

but it resolves to

::boost::multi_index::mem_fun_explicit<
  Class,Type,Type (Class::*)(),&Class::MemberFunName
>

for MSVC++ 6.0 or lower.

Header "boost/multi_index/composite_key.hpp" synopsis

namespace boost{

namespace multi_index{

template<typename Value,typename KeyFromValue0,...,typename KeyFromValuen>
struct composite_key;

template<typename CompositeKey>
struct composite_key_result;
  
// comparison operators for composite_key_result:

// OP is any of =,<,!=,>,>=,<=

template<typename CompositeKey1,typename CompositeKey2>
bool operator OP(
  const composite_key_result<CompositeKey1>& x,
  const composite_key_result<CompositeKey2>& y);

template<typename CompositeKey,typename Value0,...,typename Valuen>
bool operator OP(
  const composite_key_result<CompositeKey>& x,
  const tuple<Value0,...,Valuen>& y);

template<typename Value0,...,typename Valuen,typename CompositeKey>
bool operator OP(
  const tuple<Value0,...,Valuen>& x,
  const composite_key_result<CompositeKey>& y);

// equality functors:

template<typename Pred0,...,typename Predn>
struct composite_key_equal_to;
  
template<typename CompositeKeyResult>
struct composite_key_result_equal_to;

// comparison functors:

template<typename Compare0,...,typename Comparen>
struct composite_key_compare;
  
template<typename CompositeKeyResult>
struct composite_key_result_less;

template<typename CompositeKeyResult>
struct composite_key_result_greater;

// hash functors:

template<typename Hash0,...,typename Hashn>
struct composite_key_hash;
  
template<typename CompositeKeyResult>
struct composite_key_result_hash;

} // namespace boost::multi_index

} // namespace boost

// specializations of external functors for composite_key_result:

namespace std{

template<typename CompositeKey>
struct equal_to<boost::multi_index::composite_key_result<CompositeKey> >;

template<typename CompositeKey>
struct less<boost::multi_index::composite_key_result<CompositeKey> >;

template<typename CompositeKey>
struct greater<boost::multi_index::composite_key_result<CompositeKey> >;

} // namespace std

namespace boost{

template<typename CompositeKey>
struct hash<boost::multi_index::composite_key_result<CompositeKey> >;

} // namespace boost

Class template composite_key

composite_key is a Key Extractor returning the combined value of several key extractors whose type is specified at compile time. The returned object is of type composite_key_result<composite_key>.

template<typename Value,typename KeyFromValue0,...,typename KeyFromValuen>
struct composite_key
{
  typedef tuple<KeyFromValue0,...,KeyFromValuen> key_extractor_tuple;
  typedef Value                                  value_type;
  typedef composite_key_result<composite_key>    result_type;

  composite_key(
    const KeyFromValue0& k0=KeyFromValue0(),
    ...
    const KeyFromValuen& kn=KeyFromValuen());

  composite_key(const key_extractor_tuple& x);

  const key_extractor_tuple& key_extractors()const;
  key_extractor_tuple&       key_extractors()

  template<typename ChainedPtr>
  result_type operator()(const ChainedPtr& x)const;
  
  result_type operator()(const value_type& x)const;
  result_type operator()(const reference_wrapper<const value_type>& x)const;
  result_type operator()(const reference_wrapper<value_type>& x)const;
};

KeyFromValue0, ... , KeyFromValuen are the types of the key extractors combined into the composite key. Each of these types must be a Key Extractor from Value. At least a key extractor must be provided. The maximum number of key extractors of a composite_key instantiation is implementation defined. composite_key internally stores an object of every constituent key extractor type. composite_key<Value,KeyFromValue0,...,KeyFromValuen> is a model of:

• Key Extractor from Value,
• Key Extractor from reference_wrapper<const Value>,
• Key Extractor from reference_wrapper<Value>,
• Key Extractor from any chained pointer to const Value,
• Key Extractor from any chained pointer to Value.

composite_key members

Effects: Constructs a composite_key that stores copies of the key extractor objects supplied.

Effects: Constructs a composite_key that stores copies of the key extractor objects supplied in x.

Returns: a constant reference to a tuple holding the key extractors internally stored by the composite_key.

Returns: a reference to a tuple holding the key extractors internally stored by the composite_key.

Requires: ChainedPtr is a chained pointer type to result_type.
Returns: a result_type object dependent on *this and y, where y is the object chained-pointed to by x.

Returns: a result_type object dependent on *this and x.

Returns: a result_type object dependent on *this and x.get().

Returns: a result_type object dependent on *this and x.get().

Class template composite_key_result

This is an opaque type returned by composite_key instantiations as their extracted key.

template<typename CompositeKey>
struct composite_key_result
{
  no public interface available
};

// comparison:
  
// OP is any of =,<,!=,>,>=,<=

template<typename CompositeKey1,typename CompositeKey2>
bool operator OP(
  const composite_key_result<CompositeKey1>& x,
  const composite_key_result<CompositeKey2>& y);

template<typename CompositeKey,typename Value0,...,typename Valuen>
bool operator OP(
  const composite_key_result<CompositeKey>& x,
  const tuple<Value0,...,Valuen>& y);

template<typename Value0,...,typename Valuen,typename CompositeKey>
bool operator OP(
  const tuple<Value0,...,Valuen>& x,
  const composite_key_result<CompositeKey>& y);

Notation

Given an x of type composite_key_result<CompositeKey>, we use the following notation:

• ck(x) is the CompositeKey object associated to x,
• v(x) is the object of type CompositeKey::value_type associated to x,
• ki(x) = ck(x).key_extractors().get<i>(), that is, is the i-th key extractor of ck(x),
• xi = ki(x)(v(x)), that is, the key extracted from v(x) by the i-th key extractor,
• length(x) is the number of key extractors of ck(x).

• yi=y.get<i>(),
• length(y) is the number of elements of y.

Comparison operators

Requires: length(x)==length(y). The expression xi==yi is valid for all i in [0,length(x)).
Returns: true if and only if

xi==yi for all i in [0,length(x)).

Complexity: No more key extraction operations and comparisons are performed than those necessary for the evaluation of the expression above, starting at i==0. The evaluation is short-circuited as soon as the result is determined to be false.

Requires: The expressions xi<yi and yi<xi are valid for all i in [0,min(length(x),length(y))).
Returns: true if and only if there exists some j in the range [0,min(length(x),length(y))) such that

!(xi<yi) && !(yi<xi) for all i in [0,j),
  xj<yj.

Complexity: No more key extraction operations and comparisons are performed than those necessary for the evaluation of the expression above, starting at i==0. The evaluation is short-circuited as soon as the result is determined to be false.

(OP is any of !=, >, >=, <=.)

Requires: The expressions given below are valid (for the particular OP considered.)
Returns: true if and only if

!(x==y) (OP is !=),
  y< x  (OP is > ),
!(x< y) (OP is >=),
!(y< x) (OP is <=).

Equality

Class template composite_key_equal_to

composite_key_equal_to tests for equality between composite_key_result instantiations and between these and tuples of values, using an internally stored collection of elementary equality predicates.

template<typename Pred0,...,typename Predn>
struct composite_key_equal_to
{
  typedef tuple<Pred0,...,Predn> key_eq_tuple;

  composite_key_equal_to(
    const Pred0& p0=Pred0(),
    ...
    const Predn& pn=Predn());

  composite_key_equal_to(const key_eq_tuple& x);

  const key_eq_tuple& key_eqs()const;
  key_eq_tuple&       key_eqs();

  template<typename CompositeKey1,typename CompositeKey2>
  bool operator()(
    const composite_key_result<CompositeKey1> & x,
    const composite_key_result<CompositeKey2> & y)const;
  
  template<typename CompositeKey,typename Value0,...,typename Valuen>
  bool operator()(
    const composite_key_result<CompositeKey>& x,
    const tuple<Value0,...,Valuen>& y)const;

  template<typename Value0,...,typename Valuen,typename CompositeKey>
  bool operator()(
    const tuple<Value0,...,Valuen>& x,
    const composite_key_result<CompositeKey>& y)const;
};

Pred0, ... , Predn are the types of the equality predicates stored by composite_key_equal_to. Each of these types must be a Binary Predicate. At least an equality predicate must be provided. The maximum number of equality predicates of a composite_key_equal_to instantiation is implementation defined. composite_key_equal_to is Assignable. It is also Default Constructible if each Predi is Default Constructible.

Note that formally it is not required that the Predi types behave as equality predicates in any definite way. However, the semantics of composite_key_equal_to is well defined if this is the case, as explained in the section on the semantics of composite_key_result.

Notation

In what follows we use the same notation introduced for composite_key_result.

composite_key_equal_to members

Effects: Constructs a composite_key_equal_to that stores copies of the equality predicates supplied.

Effects: Constructs a composite_key_equal_to that stores copies of the equality predicate objects supplied in x.

Returns: a constant reference to a tuple holding the equality predicate objects internally stored by the composite_key_equal_to.

Returns: a reference to a tuple holding the equality predicate objects internally stored by the composite_key_equal_to.

Requires: length(x)==length(y). The expressions key_eqs().get<i>()(xi,yi) and key_eqs().get<i>()(yi,xi) are valid for all i in [0,length(x)).
Returns: true if and only

key_eqs().get<i>()(xi,yi) for all i in [0,length(x)).

Complexity: No more key extraction operations and comparisons are performed than those necessary for the evaluation of the expression above, starting at i==0. The evaluation is short-circuited as soon as the result is determined to be false.

Class template composite_key_result_equal_to

composite_key_result_equal_to acts as a particularization of composite_key_equal_to where all the comparison predicates supplied are instantiations of std::equal_to.

template<typename CompositeKeyResult>
struct composite_key_result_equal_to
{
  typedef CompositeKeyResult  first_argument_type;
  typedef first_argument_type second_argument_type;
  typedef bool                result_type;

  template<typename CompositeKey1,typename CompositeKey2>
  bool operator()(
    const composite_key_result<CompositeKey1> & x,
    const composite_key_result<CompositeKey2> & y)const;
  
  template<typename CompositeKey,typename Value0,...,typename Valuen>
  bool operator()(
    const composite_key_result<CompositeKey>& x,
    const tuple<Value0,...,Valuen>& y)const;

  template<typename Value0,...,typename Valuen,typename CompositeKey>
  bool operator()(
    const tuple<Value0,...,Valuen>& x,
    const composite_key_result<CompositeKey>& y)const;
};

CompositeKeyResult must be an instantiation of composite_key_result for some type composite_key<KeyFromValue0,...,KeyFromValuen>. composite_key_result_equal_to<CompositeKeyResult>::operator() is then equivalent to composite_key_equal_to<Pred0,...,Predn>::operator(), taking

Predi = std::equal_to<KeyFromValuei::result_type> for all i = 0,...,n.

In addition to the requirements on Predi imposed by composite_key_equal_to, each of these types must be Default Constructible. composite_key_result_equal_to is Default Constructible and Assignable.

Specialization of std::equal_to for composite_key results

std::equal_to<CompositeKeyResult>, for CompositeKeyResult being an instantiation of composite_key_result, has the same interface and functionality as composite_key_result_equal_to<CompositeKeyResult>.

namespace std{

template<typename CompositeKey>
struct equal_to<boost::multi_index::composite_key_result<CompositeKey> >
{
  typedef 
    boost::multi_index::composite_key_result<
      CompositeKey>                           first_argument_type;
  typedef first_argument_type                 second_argument_type;
  typedef bool                                result_type;

  template<typename CompositeKey1,typename CompositeKey2>
  bool operator()(
    const boost::multi_index::composite_key_result<CompositeKey1> & x,
    const boost::multi_index::composite_key_result<CompositeKey2> & y)const;
  
  template<typename CompositeKey,typename Value0,...,typename Valuen>
  bool operator()(
    const boost::multi_index::composite_key_result<CompositeKey>& x,
    const boost::tuple<Value0,...,Valuen>& y)const;

  template<typename Value0,...,typename Valuen,typename CompositeKey>
  bool operator()(
    const boost::tuple<Value0,...,Valuen>& x,
    const boost::multi_index::composite_key_result<CompositeKey>& y)const;
};

} // namespace std

Comparison

Class template composite_key_compare

composite_key_compare compares composite_key_result instantiations between them and with tuples of values using an internally stored collection of elementary comparison predicates.

template<typename Compare0,...,typename Comparen>
struct composite_key_compare
{
  typedef tuple<Compare0,...,Comparen> key_comp_tuple;

  composite_key_compare(
    const Compare0& c0=Compare0(),
    ...
    const Comparen& cn=Comparen());

  composite_key_compare(const key_comp_tuple& x);

  const key_comp_tuple& key_comps()const;
  key_comp_tuple&       key_comps();

  template<typename CompositeKey1,typename CompositeKey2>
  bool operator()(
    const composite_key_result<CompositeKey1> & x,
    const composite_key_result<CompositeKey2> & y)const;
  
  template<typename CompositeKey,typename Value0,...,typename Valuen>
  bool operator()(
    const composite_key_result<CompositeKey>& x,
    const tuple<Value0,...,Valuen>& y)const;

  template<typename Value0,...,typename Valuen,typename CompositeKey>
  bool operator()(
    const tuple<Value0,...,Valuen>& x,
    const composite_key_result<CompositeKey>& y)const;
};

Compare0, ... , Comparen are the types of the comparison predicates stored by composite_key_compare. Each of these types must be a Binary Predicate. At least a comparison predicate must be provided. The maximum number of comparison predicates of a composite_key_compare instantiation is implementation defined. composite_key_compare is Assignable. It is also Default Constructible if each Comparei is Default Constructible.

Note that formally it is not required that the Comparei types behave as comparison predicates in any definite way. However, the semantics of composite_key_compare is well defined if this is the case, as explained in the section on the semantics of composite_key_result.

Notation

In what follows we use the same notation introduced for composite_key_result.

composite_key_compare members

Effects: Constructs a composite_key_compare that stores copies of the comparison predicates supplied.

Effects: Constructs a composite_key_compare that stores copies of the comparison predicate objects supplied in x.

Returns: a constant reference to a tuple holding the comparison predicate objects internally stored by the composite_key_compare.

Returns: a reference to a tuple holding the comparison predicate objects internally stored by the composite_key_compare.

Requires: The expressions key_comps().get<i>()(xi,yi) and key_comps().get<i>()(yi,xi) are valid for all i in [0,min(length(x),length(y))).
Returns: true if and only if there exists some j in the range [0,min(length(x),length(y))) such that

!key_comps().get<i>()(xi,yi) && !key_comps().get<i>()(yi,xi) for all i in [0,j),
 key_comps().get<j>()(xj,yj).

Complexity: No more key extraction operations and comparisons are performed than those necessary for the evaluation of the expression above, starting at i==0. The evaluation is short-circuited as soon as the result is determined to be false.

Class template composite_key_result_less

composite_key_result_less acts as a particularization of composite_key_compare where all the comparison predicates supplied are instantiations of std::less.

template<typename CompositeKeyResult>
struct composite_key_result_less
{
  typedef CompositeKeyResult  first_argument_type;
  typedef first_argument_type second_argument_type;
  typedef bool                result_type;

  template<typename CompositeKey1,typename CompositeKey2>
  bool operator()(
    const composite_key_result<CompositeKey1> & x,
    const composite_key_result<CompositeKey2> & y)const;
  
  template<typename CompositeKey,typename Value0,...,typename Valuen>
  bool operator()(
    const composite_key_result<CompositeKey>& x,
    const tuple<Value0,...,Valuen>& y)const;

  template<typename Value0,...,typename Valuen,typename CompositeKey>
  bool operator()(
    const tuple<Value0,...,Valuen>& x,
    const composite_key_result<CompositeKey>& y)const;
};

CompositeKeyResult must be an instantiation of composite_key_result for some type composite_key<KeyFromValue0,...,KeyFromValuen>. composite_key_result_less<CompositeKeyResult>::operator() is then equivalent to composite_key_compare<Compare0,...,Comparen>::operator(), taking

Comparei = std::less<KeyFromValuei::result_type> for all i = 0,...,n.

In addition to the requirements on Comparei imposed by composite_key_compare, each of these types must be Default Constructible. composite_key_result_less is Default Constructible and Assignable.

Class template composite_key_result_greater

composite_key_result acts as a particularization of composite_key_compare where all the comparison predicates supplied are instantiations of std::greater.

template<typename CompositeKeyResult>
struct composite_key_result_greater
{
  typedef CompositeKeyResult  first_argument_type;
  typedef first_argument_type second_argument_type;
  typedef bool                result_type;

  template<typename CompositeKey1,typename CompositeKey2>
  bool operator()(
    const composite_key_result<CompositeKey1> & x,
    const composite_key_result<CompositeKey2> & y)const;
  
  template<typename CompositeKey,typename Value0,...,typename Valuen>
  bool operator()(
    const composite_key_result<CompositeKey>& x,
    const tuple<Value0,...,Valuen>& y)const;

  template<typename Value0,...,typename Valuen,typename CompositeKey>
  bool operator()(
    const tuple<Value0,...,Valuen>& x,
    const composite_key_result<CompositeKey>& y)const;
};

CompositeKeyResult must be an instantiation of composite_key_result for some type composite_key<KeyFromValue0,...,KeyFromValuen>. composite_key_result_greater<CompositeKeyResult>::operator() is then equivalent to composite_key_compare<Compare0,...,Comparen>::operator(), taking

Comparei = std::greater<KeyFromValuei::result_type> for all i = 0,...,n.

In addition to the requirements on Comparei imposed by composite_key_compare, each of these types must be Default Constructible. composite_key_result_greater is Default Constructible and Assignable.

Specialization of std::less for composite_key results

std::less<CompositeKeyResult>, for CompositeKeyResult being an instantiation of composite_key_result, has the same interface and functionality as composite_key_result_less<CompositeKeyResult>.

namespace std{

template<typename CompositeKey>
struct less<boost::multi_index::composite_key_result<CompositeKey> >
{
  typedef
    boost::multi_index::composite_key_result<
      CompositeKey>                           first_argument_type;
  typedef first_argument_type                 second_argument_type;
  typedef bool                                result_type;

  template<typename CompositeKey1,typename CompositeKey2>
  bool operator()(
    const boost::multi_index::composite_key_result<CompositeKey1> & x,
    const boost::multi_index::composite_key_result<CompositeKey2> & y)const;
  
  template<typename CompositeKey,typename Value0,...,typename Valuen>
  bool operator()(
    const boost::multi_index::composite_key_result<CompositeKey>& x,
    const boost::tuple<Value0,...,Valuen>& y)const;

  template<typename Value0,...,typename Valuen,typename CompositeKey>
  bool operator()(
    const boost::tuple<Value0,...,Valuen>& x,
    const boost::multi_index::composite_key_result<CompositeKey>& y)const;
};

} // namespace std

Specialization of std::greater for composite_key results

std::greater<CompositeKeyResult>, for CompositeKeyResult being an instantiation of composite_key_result, has the same interface and functionality as composite_key_result_greater<CompositeKeyResult>.

namespace std{

template<typename CompositeKey>
struct greater<boost::multi_index::composite_key_result<CompositeKey> >
{
  typedef
    boost::multi_index::composite_key_result<
      CompositeKey>                           first_argument_type;
  typedef first_argument_type                 second_argument_type;
  typedef bool                                result_type;

  template<typename CompositeKey1,typename CompositeKey2>
  bool operator()(
    const boost::multi_index::composite_key_result<CompositeKey1> & x,
    const boost::multi_index::composite_key_result<CompositeKey2> & y)const;
  
  template<typename CompositeKey,typename Value0,...,typename Valuen>
  bool operator()(
    const boost::multi_index::composite_key_result<CompositeKey>& x,
    const boost::tuple<Value0,...,Valuen>& y)const;

  template<typename Value0,...,typename Valuen,typename CompositeKey>
  bool operator()(
    const boost::tuple<Value0,...,Valuen>& x,
    const boost::multi_index::composite_key_result<CompositeKey>& y)const;
};

} // namespace std

Hashing

Class template composite_key_hash

composite_key_hash produces hash values for composite_key_result instantiations based on a collection of elementary hash functors.

template<typename Hash0,...,typename Hashn>
struct composite_key_hash
{
  typedef tuple<Hash0,...,Hashn> key_hasher_tuple;

  composite_key_hash(
    const Hash0& h0=Hash0(),
    ...
    const Hashn& hn=Hashn());

  composite_key_hash(const key_hasher_tuple& x);

  const key_hasher_tuple& key_hash_functions()const;
  key_hasher_tuple&       key_hash_functions();

  template<typename CompositeKey>
  std::size_t operator()(
    const composite_key_result<CompositeKey>& x)const;
  
  template<typename Value0,...,typename Valuen>
  std::size_t operator()(
    const tuple<Value0,...,Valuen>& x)const;
};

Hash0, ... , Hashn are the types of the hash functors stored by composite_key_hash. Each of these types must be a Unary Function returning a value of type std::size_t in the range [0, std::numeric_limits<std::size_t>::max()). At least a hash functor must be provided. The maximum number of hash functors of a composite_key_hash instantiation is implementation defined. composite_key_hash is Assignable. It is also Default Constructible if each Hashi is Default Constructible.

Notation

In what follows we use the same notation introduced for composite_key_result.

composite_key_hash members

Effects: Constructs a composite_key_hash that stores copies of the hash functors supplied.

Effects: Constructs a composite_key_hash that stores copies of the hash functors supplied in x.

Returns: a constant reference to a tuple holding the hash functors internally stored by the composite_key_hash.

Returns: a reference to a tuple holding the hash functors internally stored by the composite_key_hash.

Requires: length(x)==length(key_hash_functions()). The expression key_hash_functions().get<i>()(xi) is valid for all i in [0,length(x)).
Returns: A value in the range [0, std::numeric_limits<std::size_t>::max()) that solely depends on the numerical tuple

(key_hash_functions().get<0>()(x0), ... , key_hash_functions().get<N>()(xN)), with N=length(x)-1.

Class template composite_key_result_hash

composite_key_result_hash acts as a particularization of composite_key_hash where all the hash functors supplied are instantiations of boost::hash.

template<typename CompositeKeyResult>
struct composite_key_result_hash
{
  typedef CompositeKeyResult argument_type;
  typedef std::size_t        result_type;

  template<typename CompositeKey>
  std::size_t operator()(
    const composite_key_result<CompositeKey>& x)const;
  
  template<typename Value0,...,typename Valuen>
  std::size_t operator()(
     const tuple<Value0,...,Valuen>& x)const;
};

CompositeKeyResult must be an instantiation of composite_key_result for some type composite_key<KeyFromValue0,...,KeyFromValuen>. composite_key_result_hash<CompositeKeyResult>::operator() is then equivalent to composite_key_hash<Hash0,...,Hashn>::operator(), taking

Hashi = boost::hash<KeyFromValuei::result_type> for all i = 0,...,n.

In addition to the requirements on Hashi imposed by composite_key_hash, each of these types must be Default Constructible. composite_key_result_hash is Default Constructible and Assignable.

Specialization of boost::hash for composite_key results

boost::hash<CompositeKeyResult>, for CompositeKeyResult being an instantiation of composite_key_result, has the same interface and functionality as composite_key_result_hash<CompositeKeyResult>.

namespace boost{

template<typename CompositeKey>
struct hash<multi_index::composite_key_result<CompositeKey> >
{
  typedef multi_index::composite_key_result<CompositeKey> argument_type;
  typedef std::size_t                                     result_type;

  template<typename CompositeKey>
  std::size_t operator()(
    const multi_index::composite_key_result<CompositeKey>& x)const;
  
  template<typename Value0,...,typename Valuen>
  std::size_t operator()(
    const tuple<Value0,...,Valuen>& x)const;
};

} // namespace boost

Semantics of composite_key_result

The design of equality, comparison and hash operations for composite_key_result objects is based on the following rationale: a composite_key_result is regarded as a "virtual" tuple, each of its elements being the result of the corresponding elementary key extractor. Accordingly, any given operation resolves to a combination of the corresponding elementwise operations. This mapping preserves the fundamental properties of the elementary operations involved; for instance, it defines a true equivalence relation if the basic predicates induce equivalence relations themselves. We can state these facts in a formal way as follows.

Consider an instantiation of composite_key_equal_to with types Pred0, ... , Predn such that each Predi induces an equivalence relation on a certain type Ti, and let CompositeKey be a type of the form composite_key<Value,KeyFromValue0,...,KeyFromValuej>, with j <= n, such that

KeyFromValuei::result_type = Ti, for all i = 0,...,j.

tuple<Q0,...,Qj>,
composite_key_result<composite_key<K0,...,Kj> >, with Ki::result_type = Qi for all i = 0,...,j.

As for comparison, consider an instantiation of composite_key_compare with types Compare0, ... , Comparen such that each Comparei is a Strict Weak Ordering on the type Ti. Then, for a CompositeKey type defined in the same manner as above, composite_key_compare is a Strict Weak Ordering on elements of type composite_key_result<CompositeKey>, and the order induced is lexicographical. Also, the following types are Compatible Keys of composite_key_compare with respect to composite_key_result<CompositeKey>:

tuple<Q0,...,Qk>, k <= n
composite_key_result<composite_key<K0,...,Kk> >, with Ki::result_type = Qi for all i = 0,...,k.

Analogous properties hold for the equality and comparison operators of composite_key_result. Note, however, that equality is only defined for objects of the same length, whilst comparison takes the minimum length of the operands considered. Therefore, the equivalence classes induced by x==y are subsets of those associated to !(x<y)&&!(y<x).

Sequenced indices

Boost.MultiIndex reference

Compiler specifics

Revised September 5th 2005

© Copyright 2003-2005 Joaquín M López Muñoz. Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)