System.Text.RegularExpressions.RegexParser.CountCaptures C# (CSharp) Method

        internal void CountCaptures()
        {
            char ch;

            NoteCaptureSlot(0, 0);

            _autocap = 1;

            while (CharsRight() > 0)
            {
                int pos = Textpos();
                ch = MoveRightGetChar();
                switch (ch)
                {
                    case '\\':
                        if (CharsRight() > 0)
                            MoveRight();
                        break;

                    case '#':
                        if (UseOptionX())
                        {
                            MoveLeft();
                            ScanBlank();
                        }
                        break;

                    case '[':
                        ScanCharClass(false, true);
                        break;

                    case ')':
                        if (!EmptyOptionsStack())
                            PopOptions();
                        break;

                    case '(':
                        if (CharsRight() >= 2 && RightChar(1) == '#' && RightChar() == '?')
                        {
                            MoveLeft();
                            ScanBlank();
                        }
                        else
                        {
                            PushOptions();
                            if (CharsRight() > 0 && RightChar() == '?')
                            {
                                // we have (?...
                                MoveRight();

                                if (CharsRight() > 1 && (RightChar() == '<' || RightChar() == '\''))
                                {
                                    // named group: (?<... or (?'...

                                    MoveRight();
                                    ch = RightChar();

                                    if (ch != '0' && RegexCharClass.IsWordChar(ch))
                                    {
                                        //if (_ignoreNextParen)
                                        //    throw MakeException(SR.AlternationCantCapture);
                                        if (ch >= '1' && ch <= '9')
                                            NoteCaptureSlot(ScanDecimal(), pos);
                                        else
                                            NoteCaptureName(ScanCapname(), pos);
                                    }
                                }
                                else
                                {
                                    // (?...

                                    // get the options if it's an option construct (?cimsx-cimsx...)
                                    ScanOptions();

                                    if (CharsRight() > 0)
                                    {
                                        if (RightChar() == ')')
                                        {
                                            // (?cimsx-cimsx)
                                            MoveRight();
                                            PopKeepOptions();
                                        }
                                        else if (RightChar() == '(')
                                        {
                                            // alternation construct: (?(foo)yes|no)
                                            // ignore the next paren so we don't capture the condition
                                            _ignoreNextParen = true;

                                            // break from here so we don't reset _ignoreNextParen
                                            break;
                                        }
                                    }
                                }
                            }
                            else
                            {
                                if (!UseOptionN() && !_ignoreNextParen)
                                    NoteCaptureSlot(_autocap++, pos);
                            }
                        }

                        _ignoreNextParen = false;
                        break;
                }
            }

            AssignNameSlots();
        }

        // This static call constructs a RegexTree from a regular expression
        // pattern string and an option string.
        //
        // The method creates, drives, and drops a parser instance.
        internal static RegexTree Parse(String re, RegexOptions op) {
            RegexParser p;
            RegexNode root;
            String[] capnamelist;

            p = new RegexParser((op & RegexOptions.CultureInvariant) != 0 ? CultureInfo.InvariantCulture : CultureInfo.CurrentCulture);

            p._options = op;

            p.SetPattern(re);
            p.CountCaptures();
            p.Reset(op);
            root = p.ScanRegex();

            if (p._capnamelist == null)
                capnamelist = null;
            else
                capnamelist = (String[])p._capnamelist.ToArray(typeof(String));

            return new RegexTree(root, p._caps, p._capnumlist, p._captop, p._capnames, capnamelist, op);
        }