System.Security.CodeAccessPermission.Intersect C# (CSharp) Method

        public abstract IPermission Intersect(IPermission target);
        public abstract bool IsSubsetOf(IPermission target);

        internal bool CheckDemandInternal(CodeAccessPermission demand, out Exception exception)
        {
            BCLDebug.Assert(m_head != null, "m_head != null");
            for (PListNode pnext = m_head; pnext != null; pnext = pnext.next)
            {
                if (pnext.perm == null)
                {
                    // If this is a grant set or a permit only, then we should fail since null indicates the empty permission.
                    if (pnext.type == MatchChecked || pnext.type == MatchPermitOnly)
                    {
                        BCLDebug.Assert(!demand.IsSubsetOf(null), "By the time we get here, demands that are subsets of null should have been terminated");
                        exception = new SecurityException(String.Format(Environment.GetResourceString("Security_Generic"), demand.GetType().AssemblyQualifiedName));
                        return(false);
                    }

                    // If this is a deny, then we should fail since null indicates the unrestricted permission.
                    if (pnext.type == MatchDeny)
                    {
                        exception = new SecurityException(String.Format(Environment.GetResourceString("Security_Generic"), demand.GetType().AssemblyQualifiedName));
                        return(false);
                    }

                    // If this is an assert, then we should return success and terminate the stack walk since
                    // null indicates the unrestricted permission.
                    if (pnext.type == MatchAssert)
                    {
                        exception = null;
                        return(false);
                    }

                    // If this is anything else, then we should act confused.
                    // This case is unexpected.
                    BCLDebug.Assert(false, "This case should never happen");
                    exception = new InvalidOperationException(Environment.GetResourceString("InvalidOperation_InvalidState"));
                    return(false);
                }

                CodeAccessPermission cap = pnext.perm;
                switch (pnext.type)
                {
                case MatchChecked:
                case MatchPermitOnly:
                    if (!demand.IsSubsetOf(cap))
                    {
                        exception = new SecurityException(String.Format(Environment.GetResourceString("Security_Generic"), demand.GetType().AssemblyQualifiedName));
                        return(false);
                    }
                    break;

                case MatchAssert:
                    if (demand.IsSubsetOf(cap))
                    {
                        exception = null;
                        return(false);
                    }
                    break;

                case MatchDeny:
                    if (demand.Intersect(cap) != null)
                    {
                        exception = new SecurityException(String.Format(Environment.GetResourceString("Security_Generic"), demand.GetType().AssemblyQualifiedName));
                        return(false);
                    }
                    break;

                default:
                    // Illegal entry
                    exception = new InvalidOperationException(Environment.GetResourceString("InvalidOperation_InvalidState"));
                    return(false);
                }
            }

            exception = null;
            return(true);
        }