23.set.stdcxx-216.cpp

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#include <set>
#include <cassert>
 
struct Value
{
    static const unsigned magic = 0x12344321;
 
    Value (unsigned val = 0)
        : value (val),
          valid (magic)
    {
    }
 
    Value (const Value& key)
        : value (key.value),
          valid (key.magic)
    {
    }
 
    Value& operator= (const Value& rhs)
    {
        // assignment only valid from valid values
        assert (rhs.is_valid ());
 
        value = rhs.value;
        valid = rhs.valid;
        return *this;
    }
 
    ~Value ()
    {
        // destruction only allowed for valid values
        assert (is_valid ());
 
        valid = 0;
    }
 
    bool is_valid () const
    {
        return valid == magic;
    }
 
    friend
    bool operator< (const Value& lhs, const Value& rhs)
    {
        // comparing against an invalid value is forbidden
        assert (lhs.is_valid ());
        assert (rhs.is_valid ());
 
        const int lhs_is_odd = lhs.value & 1;
        const int rhs_is_odd = rhs.value & 1;
 
        // sort all even numbers in ascending order
        // followed by odd numbers in ascending order
        return   lhs_is_odd != rhs_is_odd
               ? lhs_is_odd  < rhs_is_odd
               : lhs.value   < rhs.value;
    }
 
    unsigned value;
    unsigned valid;
};
 
 
int main ()
{
    // insert at begin
    {
        std::set<Value> s;
 
        std::set<Value>::iterator i (s.begin ());
        for (unsigned n = 0; n < 10; ++n)
            s.insert (i, n);
    }
 
    // insert after last
    {
        std::set<Value> s;
 
        std::set<Value>::iterator i (s.end ());
        for (unsigned n = 0; n < 10; ++n)
            i = s.insert (i, n);
    }
 
    // insert at end
    {
        std::set<Value> s;
 
        std::set<Value>::iterator i (s.end ());
        for (unsigned n = 0; n < 10; ++n)
            s.insert (i, n);
    }
 
    return 0;
}