- Будет использовать встроенные ф-и работы со строками InStr, Mid и т.д..

Вот только не InStr и не Mid

20 WMZ и на C# я напишу тебе код и для твоего паттерна

    Function FindMatches(ByVal text As String) As List(Of MyMatch)
        Dim Result As New List(Of MyMatch)

        Dim CurrentStart As Integer = 0
        Dim CurrentLex As Integer = -1
        Dim IsMatch As Boolean = False
        Dim SubDomainLength As Integer
        Dim IsEnd As Boolean = False
        Dim ValidEnd As Integer = -1
        Dim ValidLocalEnd As Integer = -1

        For i As Integer = 0 To text.Length - 1
            Dim C As Char = text(i)

            If Not IsMatch OrElse CurrentLex = 0 Then
                If (C >= "0"c AndAlso C <= "9"c) OrElse (C >= "A"c AndAlso C <= "Z"c) OrElse (C >= "a"c AndAlso C <= "z"c) OrElse C = "-"c OrElse C = "."c OrElse C = "_"c Then
                    If Not IsMatch Then
                        IsMatch = True
                        CurrentStart = i
                        ValidEnd = -1
                        CurrentLex = 0
                    End If
                    GoTo ok
                End If
            End If

            If IsMatch AndAlso CurrentLex = 0 Then
                If C = "@"c Then
                    CurrentLex = 1
                    GoTo ok
                End If
            End If

            If IsMatch AndAlso CurrentLex = 1 OrElse CurrentLex = 2 Then
                If (C >= "0"c AndAlso C <= "9"c) OrElse (C >= "A"c AndAlso C <= "Z"c) OrElse (C >= "a"c AndAlso C <= "z"c) OrElse C = "-"c Then
                    CurrentLex = 2
                    GoTo ok
                End If
            End If

            If IsMatch AndAlso CurrentLex = 2 Then
                If C = "."c Then
                    CurrentLex = 3
                    SubDomainLength = 0
                    IsEnd = True
                    GoTo ok
                End If
            End If



            If IsMatch AndAlso CurrentLex = 3 OrElse CurrentLex = 4 Then
                If (C >= "0"c AndAlso C <= "9"c) OrElse (C >= "A"c AndAlso C <= "Z"c) OrElse (C >= "a"c AndAlso C <= "z"c) OrElse C = "-"c Then
                    CurrentLex = 4
                    SubDomainLength += 1
                    If C = "-"c Then
                        IsEnd = False
                    Else
                        If SubDomainLength >= 2 AndAlso SubDomainLength <= 4 AndAlso IsEnd Then
                            ValidLocalEnd = i
                        Else
                            ValidLocalEnd = -1
                        End If
                    End If
                    GoTo ok
                End If
            End If

            If IsMatch AndAlso CurrentLex = 4 Then
                If C = "."c Then
                    If IsEnd AndAlso ValidLocalEnd <> -1 Then
                        ValidEnd = ValidLocalEnd
                    End If
                    IsEnd = True
                    ValidLocalEnd = -1
                    SubDomainLength = 0
                    CurrentLex = 3
                    GoTo ok
                End If
            End If

            If IsMatch AndAlso IsEnd AndAlso ValidLocalEnd <> -1 AndAlso CurrentLex = 4 Then
                Result.Add(New MyMatch(text.Substring(CurrentStart, ValidLocalEnd - CurrentStart + 1), CurrentStart))
                IsMatch = False
                GoTo ok
            End If

            If IsMatch AndAlso ValidEnd <> -1 AndAlso CurrentLex = 4 Then
                Result.Add(New MyMatch(text.Substring(CurrentStart, ValidEnd - CurrentStart + 1), CurrentStart))
                IsMatch = False
                GoTo ok
            End If

            IsMatch = False
ok:
        Next
        If IsMatch AndAlso IsEnd AndAlso ValidLocalEnd <> -1 AndAlso CurrentLex = 4 Then
            Result.Add(New MyMatch(text.Substring(CurrentStart, ValidLocalEnd - CurrentStart + 1), CurrentStart))
        End If

        If IsMatch AndAlso ValidEnd <> -1 AndAlso CurrentLex = 4 Then
            Result.Add(New MyMatch(text.Substring(CurrentStart, ValidEnd - CurrentStart + 1), CurrentStart))
        End If
        Return Result
    End Function

Вот я и прошу показать мне, ламеру бестолковому, как это делается с помощью InStr & Mid, чтобы это было быстрее регэкспа.