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Boost.MultiIndex Key extraction reference



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Key Extractors

Key extraction classes are used by key-based indices to obtain the indexing keys from the elements of a multi_index_container. A CopyConstructible and CopyAssignable 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),
for every k1, k2 of type const KeyFromValue, and ca of type const Type&.

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)),
for every k1 of type const KeyFromValue and a of type Type&.

Boost.MultiIndex provides six general-purpose key extractors:

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

that is, chained pointers are arbitrary compositions of pointer-like objects ultimately dereferencing to values of Type& or boost::reference_wrapper<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/global_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;

  // only provided if const ChainedPtr& is not convertible to const 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:

identity members

template<typename ChainedPtr> Type& operator()(const ChainedPtr& x)const;
Requires: ChainedPtr is a chained pointer type to Type.
Returns: a reference to the object chained-pointed to by x.
const Type& operator()(const Type& x)const;
Returns: x.
Type& operator()(Type& x)const;
Returns: x.
const Type& operator()(const reference_wrapper<const Type>& x)const;
Returns: x.get().
Type& operator()(const reference_wrapper<typename remove_const<Type>::type>& x)const;
Returns: x.get().
Type& operator()(const reference_wrapper<Type>& x)const;
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; // deprecated

#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;

  // only provided if const ChainedPtr& is not convertible to const Class&
  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:

member members

template<typename ChainedPtr> Type& operator()(const ChainedPtr& x)const;
Requires: ChainedPtr is a chained pointer type to Type.
Returns: a reference to the object chained-pointed to by x.
const Type& operator()(const Class& x)const;
Returns: x.*PtrToMember.
Type& operator()(Class& x)const;
Returns: x.*PtrToMember.
const Type& operator()(const reference_wrapper<const Class>& x)const;
Returns: x.get().*PtrToMember.
Type& operator()(const reference_wrapper<Class>& x)const;
Returns: x.get().*PtrToMember.

Class template member_offset

member_offset was designed to overcome limitations of some legacy compilers and its use is currently deprecated. Refer to a former version of Boost.MultiIndex for further information.

Macro BOOST_MULTI_INDEX_MEMBER

BOOST_MULTI_INDEX_MEMBER(Class,Type,MemberName)

This macro was designed as a portability mechanism for legacy compilers where member could not be supported. As such it is no longer needed in modern environments, though some users might still prefer it to plain member because it provides a slightly more concise syntax.

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; // deprecated

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

#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;

  // only provided if const ChainedPtr& is not convertible to const Class&
  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:

const_mem_fun members

template<typename ChainedPtr> Type operator()(const ChainedPtr& x)const;
Requires: ChainedPtr is a chained pointer type to Type.
Returns: (y.*PtrToMemberFunction)(), where y is the object chained-pointed to by x.
Type operator()(const Class& x)const;
Returns: (x.*PtrToMemberFunction)().
Type operator()(const reference_wrapper<const Class>& x)const;
Returns: (x.get().*PtrToMemberFunction)().
Type operator()(const reference_wrapper<Class>& x)const;
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;

  // only provided if ChainedPtr& is not convertible to Class&
  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:

mem_fun members

template<typename ChainedPtr> Type operator()(const ChainedPtr& x)const;
Requires: ChainedPtr is a chained pointer type to Type.
Returns: (y.*PtrToMemberFunction)(), where y is the object chained-pointed to by x.
Type operator()(Class& x)const;
Returns: (x.*PtrToMemberFunction)().
Type operator()(const reference_wrapper<Class>& x)const;
Returns: (x.get().*PtrToMemberFunction)().

Class templates const_mem_fun_explicit and mem_fun_explicit

These extractors were provided as a workaround for MSVC++ 6.0 and are now deprecated. Refer to a former version of Boost.MultiIndex for further information.

Macros BOOST_MULTI_INDEX_CONST_MEM_FUN and BOOST_MULTI_INDEX_MEM_FUN

BOOST_MULTI_INDEX_CONST_MEM_FUN(Class,Type,MemberFunName)
BOOST_MULTI_INDEX_MEM_FUN(Class,Type,MemberFunName)

Portability macros for usage of const_mem_fun and mem_fun. Although no longer needed in modern compilers, some users might still decide to resort to them as they provide a slightly more concise syntax.

Header "boost/multi_index/global_fun.hpp" synopsis

namespace boost{

namespace multi_index{

template<class Value,typename Type,Type (*PtrToFunction)(Value)>
struct global_fun;

} // namespace boost::multi_index 

} // namespace boost

Class template global_fun

global_fun is a Key Extractor based on a given global or static member function accepting the base type as argument and returning the associated key.

template<class Value,typename Type,Type (*PtrToFunction)(Value)>
struct global_fun
{
  typedef typename remove_reference<Type>::type result_type;

  // Only provided under the following circumstances:
  //   - If Value is a reference to a constant type, only provided
  //     when const ChainedPtr& is not convertible to Value;
  //   - if Value is a reference to a non-const type, only provided
  //     when ChainedPtr& is not convertible to Value;
  //   - else, only provided when const ChainedPtr& is not
  //     convertible to const Value&.
  Type operator()(const ChainedPtr& x)const;
  
  // only provided if Value is a reference type
  Type operator()(Value x)const;

  // only provided if Value is not a reference type
  Type operator()(const Value& x)const;

  // only provided if Value is not a reference type
  Type operator()(const reference_wrapper<const Value>& x)const;

  // only provided if Value is a reference type
  Type operator()(
    const reference_wrapper<
      remove_reference<Value>::type>& x)const;

  // only provided if Value is not a reference type or is
  // a reference to a constant type
  Type operator()(
    const reference_wrapper<
      typename remove_const<
        typename remove_reference<Value>::type>::type>& x)const;
};

PtrToFunction specifies the particular function used to extract the key of type Type from some BaseType. global_fun supports the following function signatures:

global_fun<Type,Value,PtrToFunction> is a model of: When Value is BaseType or const BaseType&, global_fun<Type,Value,PtrToFunction> is also a model of:

global_fun members

template<typename ChainedPtr> Type operator()(const ChainedPtr& x)const;
Requires: ChainedPtr is a chained pointer type to Value.
Returns: PtrToFunction)(y), where y is the object chained-pointed to by x.
Type operator()(Value x)const;
Returns: PtrToFunction(x).
Type operator()(const Value& x)const;
Returns: PtrToFunction(x).
Type operator()(const reference_wrapper<const Value>& x)const;
Returns: PtrToFunction(x.get()).
Type operator()(
  const reference_wrapper<remove_reference<Value>::type>& x)const;
Returns: PtrToFunction(x.get()).
Type operator()(
  const reference_wrapper<
    typename remove_const<
      typename remove_reference<Value>::type>::type>& x)const;
Returns: PtrToFunction(x.get()).

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; // deprecated

// comparison functors:

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

template<typename CompositeKeyResult>
struct composite_key_result_greater;  // deprecated

// hash functors:

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

} // 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()

  // only provided if const ChainedPtr& is not convertible to const value_type&
  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:

composite_key members

composite_key(
  const KeyFromValue0& k0=KeyFromValue0(),
  ...
  const KeyFromValuen& kn=KeyFromValuen());
Effects: Constructs a composite_key that stores copies of the key extractor objects supplied.
composite_key(const key_extractor_tuple& x);
Effects: Constructs a composite_key that stores copies of the key extractor objects supplied in x.
const key_extractor_tuple& key_extractors()const;
Returns: a constant reference to a tuple holding the key extractors internally stored by the composite_key.
key_extractor_tuple& key_extractors();
Returns: a reference to a tuple holding the key extractors internally stored by the composite_key.
template<typename ChainedPtr>
result_type operator()(const ChainedPtr& x)const;
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.
result_type operator()(const value_type& x)const;
Returns: a result_type object dependent on *this and x.
result_type operator()(const reference_wrapper<const value_type>& x)const;
Returns: a result_type object dependent on *this and x.get().
result_type operator()(const reference_wrapper<value_type>& x)const;
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);
CompositeKey is the composite_key instantiation to which the composite_key_result type is associated. Objects of type composite_key_result returned by a composite key must be always treated as temporary, i.e. they should not be stored or copied. composite_key_result is not guaranteed to be DefaultConstructible or CopyAssignable. Every object of type composite_key_result<CompositeKey> is internally associated to the CompositeKey from which it is returned and the object of type CompositeKey::value_type to which the composite key was applied.

Notation

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

Also, if y is a tuple of values, we define:

Comparison operators

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

(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 binary predicates stored by composite_key_equal_to. Each of these predicates must be CopyConstructible and CopyAssignable. 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 CopyConstructible and CopyAssignable. It is also DefaultConstructible if each Predi is DefaultConstructible in its turn.

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

composite_key_equal_to(
  const Pred0& p0=Pred0(),
  ...
  const Predn& pn=Predn());
Effects: Constructs a composite_key_equal_to that stores copies of the equality predicates supplied.
composite_key_equal_to(const key_eq_tuple& x);
Effects: Constructs a composite_key_equal_to that stores copies of the equality predicate objects supplied in x.
const key_eq_tuple& key_eqs()const;
Returns: a constant reference to a tuple holding the equality predicate objects internally stored by the composite_key_equal_to.
key_eq_tuple& key_eqs();
Returns: a reference to a tuple holding the equality predicate objects internally stored by the composite_key_equal_to.
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;
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

Deprecated. Use std::equal_to<CompositeKeyResult> instead.

Specialization of std::equal_to for composite_key results

std::equal_to<CompositeKeyResult>, with CompositeKeyResult an instantiation of composite_key_result, behaves as a particularization of composite_key_equal_to where all the comparison predicates supplied are instantiations of std::equal_to.

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

CompositeKeyResult must be an instantiation of composite_key_result for some type composite_key<KeyFromValue0,...,KeyFromValuen>. std::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 DefaultConstructible. std::equal_to<CompositeKeyResult> is DefaultConstructible, CopyConstructible and CopyAssignable.

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;

  template<typename CompositeKey,typename Value>
  bool operator()(
    const composite_key_result<CompositeKey>& x,const Value& y)const;

  template<typename Value,typename CompositeKey>
  bool operator()(
    const Value& x,const composite_key_result<CompositeKey>& y)const;
};

Compare0, ... , Comparen are the types of the comparison binary predicates stored by composite_key_compare. Each of these predicates must be CopyConstructible and CopyAssignable. 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 CopyConstructible and CopyAssignable. It is also DefaultConstructible if each Comparei is DefaultConstructible in its turn.

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

composite_key_compare(
  const Compare0& c0=Compare0(),
  ...
  const Comparen& cn=Comparen());
Effects: Constructs a composite_key_compare that stores copies of the comparison predicates supplied.
composite_key_compare(const key_comp_tuple& x);
Effects: Constructs a composite_key_compare that stores copies of the comparison predicate objects supplied in x.
const key_comp_tuple& key_comps()const;
Returns: a constant reference to a tuple holding the comparison predicate objects internally stored by the composite_key_compare.
key_comp_tuple& key_comps();
Returns: a reference to a tuple holding the comparison predicate objects internally stored by the composite_key_compare.
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;
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.
template<typename CompositeKey,typename Value>
bool operator()(
  const composite_key_result<CompositeKey>& x,const Value& y)const;
Effects:
return operator()(x,make_tuple(cref(y)));

template<typename Value,typename CompositeKey>
bool operator()(
  const Value& x,const composite_key_result<CompositeKey>& y)const;
Effects:
return operator()(make_tuple(cref(x)),y);

Class template composite_key_result_less

Deprecated. Use std::less<CompositeKeyResult> instead.

Class template composite_key_result_greater

Deprecated. Use std::greater<CompositeKeyResult> instead.

Specialization of std::less for composite_key results

std::less<CompositeKeyResult>, with CompositeKeyResult an instantiation of composite_key_result, behaves as a particularization of composite_key_compare where all the comparison predicates supplied are instantiations of std::less.

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;

  template<typename CompositeKey,typename Value>
  bool operator()(
    const boost::multi_index::composite_key_result<CompositeKey>& x,
    const Value& y)const;

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

} // namespace std

CompositeKeyResult must be an instantiation of composite_key_result for some type composite_key<KeyFromValue0,...,KeyFromValuen>. std::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 DefaultConstructible. std::less<CompositeKeyResult> is CopyConstructible, CopyConstructible and CopyAssignable.

Specialization of std::greater for composite_key results

std::greater<CompositeKeyResult>, with CompositeKeyResult an instantiation of composite_key_result, behaves as a particularization of composite_key_compare where all the comparison predicates supplied are instantiations of std::greater.

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;

  template<typename CompositeKey,typename Value>
  bool operator()(
    const boost::multi_index::composite_key_result<CompositeKey>& x,
    const Value& y)const;

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

} // namespace std

CompositeKeyResult must be an instantiation of composite_key_result for some type composite_key<KeyFromValue0,...,KeyFromValuen>. std::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 DefaultConstructible. std::greater<CompositeKeyResult> is CopyConstructible, CopyConstructible and CopyAssignable.

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 unary function objects stored by composite_key_hash. Each of these objects must be CopyConstructible and CopyAssignable and return 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 CopyConstructible and CopyAssignable. It is also DefaultConstructible if each Hashi is DefaultConstructible in its turn.

Notation

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

composite_key_hash members

composite_key_hash(
  const Hash0& h0=Hash0(),
  ...
  const Hashn& hn=Hashn());
Effects: Constructs a composite_key_hash that stores copies of the hash functors supplied.
composite_key_hash(const key_hasher_tuple& x);
Effects: Constructs a composite_key_hash that stores copies of the hash functors supplied in x.
const key_hasher_tuple& key_hash_functions()const;
Returns: a constant reference to a tuple holding the hash functors internally stored by the composite_key_hash.
key_hasher_tuple& key_hash_functions();
Returns: a reference to a tuple holding the hash functors internally stored by the composite_key_hash.
template<typename CompositeKey>
bool operator()(
  const composite_key_result<CompositeKey>& x)const;
template<typename Value0,...,typename Valuen>
bool operator()(
  const tuple<Value0,...,Valuen>& x)const;
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

Deprecated. Use boost::hash<CompositeKeyResult> instead.

Specialization of boost::hash for composite_key results

boost::hash<CompositeKeyResult>, with CompositeKeyResult an instantiation of composite_key_result, behaves as a particularization of composite_key_hash where all the hash functors supplied are instantiations of boost::hash.

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

CompositeKeyResult must be an instantiation of composite_key_result for some type composite_key<KeyFromValue0,...,KeyFromValuen>. boost::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 DefaultConstructible. boost::hash<CompositeKeyResult> is DefaultConstructible, CopyConstructible and CopyAssignable.

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.
Then, composite_key_equal_to induces an equivalence relation on elements of type composite_key_result<CompositeKey>; such two objects are equivalent if all its elementary key extractor values are also equivalent. Additionally, given an instantiation composite_key_hash<Hash0,...,Hashj>, the following types are Compatible Keys of (composite_key_hash, composite_key_equal_to) with respect to composite_key_result<CompositeKey>:
tuple<Q0,...,Qj>,
composite_key_result<composite_key<K0,...,Kj> >, with Ki::result_type = Qi for all i = 0,...,j.
provided that each Qi is either Ti or a Compatible Key of (Hashi, Predi).

As for comparison, consider an instantiation of composite_key_compare with types Compare0, ... , Comparen such that each Comparei induces a strict weak ordering on the type Ti. Then, for a CompositeKey type defined in the same manner as above, composite_key_compare induces 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.
provided that In this case, the comparison is done lexicographically only on the first 1+min(j,k) elements.

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).




Revised July 7th 2013

© Copyright 2003-2013 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)