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c++boostboost-multi-index

The difference between modify and modify_key in boost multi_index_container

What is the difference between modify and modify_key in boost multi_index_container. I read their documentation both and I can't seem to find the difference between the usages of both.

Link to the documentation

Solution

  • modify_key is a variation of modify that saves you some typing when the only part of the element you want to change is the key itself. For instance, if I define a multi_index_container such as:

    struct element
{
  int x;
  int y;
};

using namespace boost::multi_index;

using container=multi_index_container<
  element,
  indexed_by<
    ordered_unique<member<element,int,&element::x>>
  >
>;

container c=...;

    Then the following:

    auto it=...;
c.modify(it,[](element& e){e.x=3;});

    can be written with modify_key as

    auto it=...;
c.modify_key(it,[](int& x){x=3;});