C++ Permutations

template<typename T>
void permute( std::vector<T> nums, void (*function)( std::vector<T>& ), int length = -1 )
{
	if( length < 0 || length > nums.size() )
		length = nums.size();
	std::function<void( int )> genPerms;
	std::vector<T> perm( length, 0 );
	std::vector<bool> used( length, false );

	genPerms = [&function, &length, &nums, &perm, &used, &genPerms]( int n )
	{
		if( length == n )
		{
			function( perm );
		} else
		{
			for( int i = 0; i < nums.size(); i++ )
			{
				if( used[i] )
					continue;
				perm[n] = nums[i];
				used[i] = true;
				genPerms( n+1 );
				used[i] = false;
			}
		}
	};

	genPerms( 0 );
}