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## Class abstract_variables_map

boost::program_options::abstract_variables_map

## Synopsis

    // In header: <boost/program_options/variables_map.hpp>

    class abstract_variables_map {
    public:
      // construct/copy/destruct
      abstract_variables_map();
      abstract_variables_map(const abstract_variables_map *);
      ~abstract_variables_map();

      // public member functions
      const variable_value & operator[](const std::string &) const;
      void next(abstract_variables_map *);

      // private member functions
      virtual const variable_value & get(const std::string &) const = 0;
    };

## Description

Implements string->string mapping with convenient value casting facilities.

### `abstract_variables_map` public construct/copy/destruct

1.     abstract_variables_map();

2.     abstract_variables_map(const abstract_variables_map * next);

3.     ~abstract_variables_map();

### `abstract_variables_map` public member functions

1.     const variable_value & operator[](const std::string & name) const;

   Obtains the value of variable 'name', from *this and possibly from the chain of variable maps.

   - if there's no value in *this.

     - if there's next variable map, returns value from it

     - otherwise, returns empty value

   - if there's defaulted value

     - if there's next varaible map, which has a non-defauled value, return that

     - otherwise, return value from *this

   - if there's a non-defauled value, returns it.

2.     void next(abstract_variables_map * next);

   Sets next variable map, which will be used to find variables not found in *this.

### `abstract_variables_map` private member functions

1.     virtual const variable_value & get(const std::string & name) const = 0;

   Returns value of variable 'name' stored in *this, or empty value otherwise.