/// <summary>
        /// Sets an individual policy.
        /// </summary>
        /// <param name="policyInterface">The <see cref="Type"/> of the policy.</param>
        /// <param name="policy">The policy to be registered.</param>
        /// <param name="buildKey">The key the policy applies.</param>
        public void Set(Type policyInterface,
                        IBuilderPolicy policy,
                        object buildKey)
        {
            lock (lockObject)
            {
                Dictionary<PolicyKey, IBuilderPolicy> newPolicies = ClonePolicies(); // takes a huge amount of % time
                newPolicies[new PolicyKey(policyInterface, buildKey)] = policy;
                SwapPolicies(newPolicies);
            }
        }