| Kea 3.0.2-git

isc::dhcp::KeyFromKeyExtractor< KeyExtractor1, KeyExtractor2 > Class Template Reference

Utility class which cascades two key extractors. More...

`#include <key_from_key.h>`

## Public Types
typedef KeyExtractor1::result_type | result_type

## Public Member Functions
| KeyFromKeyExtractor ()
| Constructor.
template<typename T>
result_type | operator() (T &arg) const
| Extract key value from the object hierarchy.

## Detailed Description

template<typename KeyExtractor1, typename KeyExtractor2>
class isc::dhcp::KeyFromKeyExtractor< KeyExtractor1, KeyExtractor2 >

Utility class which cascades two key extractors.

The key extractor (a.k.a. key extraction class) is used by the key-based indices to obtain the indexing keys from the elements of a multi_index_container. The standard key extractors can be used to retrieve indexing key values by accessing members or methods exposed by the elements (objects or structures) stored in a multi_index_container. For example, if a container holds objects of type A, then the public members of object A or its accessors can be used by the standard extractor classes such as "member" or "const_mem_fun" respectively. Assume more complex scenario, where multi_index_container holds objects of a type A, object A exposes its public member B, which in turn exposes the accessor function returning object C. One may want to use the value C (e.g. integer) to index objects A in the container. This can't be solved by using standard key extractors because object C is nested in B and thus it is not directly accessible from A. However, it is possible to specify two distinct key extractors, one used to extract value C from B, another one to extract value B from A. These two extractors can be then wrapped by another key extractor which can be used to obtain index key C from object A. This key extractor is implemented as a functor class. The functor calls functors specified as template parameters to retrieve the index value from the cascaded structure.

Template Parameters

  KeyExtractor1 | extractor used to extract the key value from the object containing it.
  KeyExtractor2 | extractor used to extract the nested object containing a key.

Definition at line 45 of file key_from_key.h.

## Member Typedef Documentation

## ◆ result_type

template<typename KeyExtractor1, typename KeyExtractor2>

typedef KeyExtractor1::result_type isc::dhcp::KeyFromKeyExtractor< KeyExtractor1, KeyExtractor2 >::result_type

Definition at line 47 of file key_from_key.h.

## Constructor & Destructor Documentation

## ◆ KeyFromKeyExtractor()

template<typename KeyExtractor1, typename KeyExtractor2>

isc::dhcp::KeyFromKeyExtractor< KeyExtractor1, KeyExtractor2 >::KeyFromKeyExtractor | ( |  | ) |
| inline

Constructor.

Definition at line 50 of file key_from_key.h.

## Member Function Documentation

## ◆ operator()()

template<typename KeyExtractor1, typename KeyExtractor2>
template<typename T>

result_type isc::dhcp::KeyFromKeyExtractor< KeyExtractor1, KeyExtractor2 >::operator() | ( | T & | arg | ) | const
| inline

Extract key value from the object hierarchy.

Parameters

  arg | the key value.

Template Parameters

  key | value type.

Definition at line 59 of file key_from_key.h.

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

- key_from_key.h