Partial const on struct

[muse1987]

Hi. I have a problem with const data types. I have a template structure named pair

template <class K, class V>
struct pair
{
	K key;
	V value;

	pair() : key(), value() {}
	pair( K const& k, V const& v ) : key(k), value(v) {}
};

Then, I wanted to declare a variable where only 'key' member is constant. So I wrote

pair<int const, int> X;

The problem is, I can't assign pair<int, int> to that variable. So I changed the structure like this

template <class K, class V>
struct pair
{
	K key;
	V value;

	pair() : key(), value() {}
	pair( K const& k, V const& v ) : key(k), value(v) {}

	operator pair<K const, V> const& () const
		{ return *reinterpret_cast<pair<K const, V> const*>(this); }

	operator pair<K const, V>& ()
		{ return *reinterpret_cast<pair<K const, V>*>(this); }
};


pair<int, int> P;
pair<int const, int>& X = P;	// Now I can do this

My question is : Is this regular way? And if not, what would be better? So far I tried to avoid reinterpret_cast as long as possible.

Any information would be much appreciated.
Thanks