map

Description

map is an Associative Sequence of heteregenous typed data elements. Each element is a key/data pair (see fusion::pair) where the key has no data (type only). Type identity is used to impose an equivalence relation on keys. A map may contain at most one element for each key. Membership testing and element key lookup has constant runtime complexity (see Overloaded Functions).

Header

#include <boost/fusion/container/map.hpp>
#include <boost/fusion/include/map.hpp>
#include <boost/fusion/container/map/map_fwd.hpp>
#include <boost/fusion/include/map_fwd.hpp>

Synopsis

template <
    typename T0 = unspecified
  , typename T1 = unspecified
  , typename T2 = unspecified
    ...
  , typename TN = unspecified
>
struct map;

The variadic class interface accepts 0 to FUSION_MAX_MAP_SIZE elements, where FUSION_MAX_MAP_SIZE is a user definable predefined maximum that defaults to 10. Example:

map<pair<int, char>, pair<char, char>, pair<double, char> >

You may define the preprocessor constant FUSION_MAX_MAP_SIZE before including any Fusion header to change the default. Example:

#define FUSION_MAX_MAP_SIZE 20

Template parameters

Parameter	Description	Default
`T0`...`TN`	Element types	unspecified-type

Model of

Notation

M: A map type
m: An instance of map
e0...en: Heterogeneous key/value pairs (see fusion::pair)
s: A Forward Sequence

Expression Semantics

Semantics of an expression is defined only where it differs from, or is not defined in Random Access Sequence and Associative Sequence.

Expression	Semantics
`M()`	Creates a map with default constructed elements.
`M(e0, e1,... en)`	Creates a map with element pairs `e0`...`en`.
`M(s)`	Copy constructs a map from a Forward Sequence `s`.
`m = s`	Assigns to a map, `m`, from a Forward Sequence `s`.

Example

typedef map<
    pair<int, char>
  , pair<double, std::string> >
map_type;

map_type m(
    make_pair<int>('X')
  , make_pair<double>("Men"));

std::cout << at_key<int>(m) << std::endl;
std::cout << at_key<double>(m) << std::endl;