RE: [boost] Challenge: bit_vector/bit_string

From: Aleksey Gurtovoy (alexy_at_[hidden])
Date: 2001-05-11 07:07:14

Beman Dawes wrote:
> Good question. I don't know the answer.  Does anyone have real-world 
> examples (NOT GUESSES!) as to how people are using vector<bool>?

Below is one of such, almost unvarnished :). The code is pretty clean, so I
won't go into much explanation.. more examples to come, though :)

#include <vector>
#include <iostream>

//------------------------ real-world part
----------------------------------

// 'counters_pool' class keeps track of used numbers in interval 
// [0..max_requested_so_far]; every next value requested from pool
// will be the least unused number in the interval

struct counters_pool
    {
    typedef std::vector<bool>       values_pool;
    typedef values_pool::size_type  value_type;
    
    value_type next_value()
        {
        values_pool::iterator i = std::find(pool_.begin(), pool_.end(),
false);
        if (i != pool_.end())
            {
            *i = true;
            return i - pool_.begin();
            }
        pool_.push_back(true);
        return pool_.size() - 1;
        }

    void put_back( value_type v ) { pool_[v] = false; }
        
    private:
        values_pool pool_;
    };

// per-class "smart" objects counter

template<class T>
struct smart_counter
    {
    typedef counters_pool::value_type value_type;
    smart_counter() : value_( pool_.next_value() ) {}
    ~smart_counter() { pool_.put_back( value_ ); }
    
    value_type value() const { return value_; }
    operator value_type() const { return value(); }
   
    private:
        static counters_pool pool_;
        const value_type value_;
    };

template<class T>
counters_pool smart_counter<T>::pool_;

//------------------- my usage example
--------------------------------------

struct window
    {
    smart_counter<window> counter;
    };

// program output:
// 0121

int main()
    {
    window m0;
    std::cout << m0.counter;
    if (true)
        {
        window m1;
        std::cout << m1.counter;
        window m2;
        std::cout << m2.counter;
        }

    window m3;
    std::cout << m3.counter;
    return 0;
    }

Aleksey