Yield/Iterator/IEnumerable - і ці люди забороняли нам багато років колупатися у носі?

   1:  Module Module1

   2:      

   3:      Sub Main()

   4:          

   5:          ' Output: A1,3,A2,5,A3,8,A4

   6:          For Each number As Integer In SomeNumbers()

   7:              Debug.Print(number)

   8:          Next

   9:   

  10:          ' Output: B1,2,B2,B1,4,B2,B1,8,B2,B1,16,B2,B1,32,B2,B1,64,B2,B1,128,B2,B1,256,B2

  11:          For Each number In Power(2, 8)

  12:              Debug.Print(number)

  13:          Next

  14:   

  15:          ' Output: C1,Sun,C2,C1,Mon,C2,C1,Tue,C2,C1,Wed,C2,C1,Thu,C2,C1,Fri,C2,C1,Sat,C2

  16:          Dim days As New DaysOfTheWeek()

  17:          For Each day As String In days

  18:              Debug.Print(day)

  19:          Next

  20:   

  21:          ' Output: D1,1,D2,2,D3

  22:          Dim iterateSequence = Iterator Function() _

  23:                        As IEnumerable(Of Integer)

  24:                                    Debug.Print("D1")

  25:                                    Yield 1

  26:                                    Debug.Print("D2")

  27:                                    Yield 2

  28:                                    Debug.Print("D3")

  29:                                End Function

  30:   

  31:          For Each number As Integer In iterateSequence()

  32:              Debug.Print(number)

  33:          Next

  34:   

  35:   

  36:          ' Output: E1,E2,E7,E3,E4,5,E5,E4,6,E5,E4,7,E5,E4,8,E5,E4,9,E5,E4,10,E5,E6

  37:          For Each number As Integer In GetSequence(5, 10)

  38:              Debug.Print(number)

  39:          Next

  40:  

  41:          ' Output: F2,F1,F7,Tadpole  400,F3,F1,F7,Pinwheel  25,F4,F1,F7,Milky Way  0,F5,F1,F7,Andromeda  3,F6

  42:          Dim theGalaxies As New Galaxies

  43:          For Each theGalaxy In theGalaxies.NextGalaxy

  44:              Debug.Print("F7")

  45:              With theGalaxy

  46:                  Debug.Print(.Name & "  " & .MegaLightYears)

  47:              End With

  48:          Next

  49:          Console.ReadKey()

  50:   

  51:      End Sub

  52:   

  53:      Private Iterator Function SomeNumbers() As System.Collections.IEnumerable

  54:          Debug.Print("A1")

  55:          Yield 3

  56:          Debug.Print("A2")

  57:          Yield 5

  58:          Debug.Print("A3")

  59:          Yield 8

  60:          Debug.Print("A4")

  61:      End Function

  62:   

  63:      Private Iterator Function Power(ByVal base As Integer, ByVal highExponent As Integer) _

  64:          As System.Collections.Generic.IEnumerable(Of Integer)

  65:   

  66:          Dim result = 1

  67:          For counter = 1 To highExponent

  68:              result = result * base

  69:              Debug.Print("B1")

  70:              Yield result

  71:              Debug.Print("B2")

  72:          Next

  73:      End Function

  74:   

  75:      Private Function GetSequence(ByVal low As Integer, ByVal high As Integer) As IEnumerable

  76:          Debug.Print("E1")

  77:          If low < 1 Then

  78:              Throw New ArgumentException("E!")

  79:          End If

  80:          Debug.Print("E2")

  81:          '  

  82:          Dim iterateSequence = Iterator Function() As IEnumerable

  83:                                    Debug.Print("E3")

  84:                                    For index = low To high

  85:                                        Debug.Print("E4")

  86:                                        Yield index

  87:                                        Debug.Print("E5")

  88:                                    Next

  89:                                    Debug.Print("E6")

  90:                                End Function

  91:          Debug.Print("E7")

  92:          Return iterateSequence()

  93:      End Function

  94:   

  95:   

  96:  End Module

  97:   

  98:   

  99:  Public Class DaysOfTheWeek

 100:      Implements IEnumerable

 101:   

 102:      Public days = New String() {"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"}

 103:   

 104:      Public Iterator Function GetEnumerator() As IEnumerator Implements IEnumerable.GetEnumerator

 105:          

 106:          For i As Integer = 0 To days.Length - 1

 107:              Debug.Print("C1")

 108:              Yield days(i)

 109:              Debug.Print("C2")

 110:          Next

 111:      End Function

 112:  End Class

 113:   

 114:  Public Class Galaxies

 115:      Public ReadOnly Iterator Property NextGalaxy _

 116:          As System.Collections.Generic.IEnumerable(Of Galaxy)

 117:          Get

 118:              Debug.Print("F2")

 119:              Yield New Galaxy With {.Name = "Tadpole", .MegaLightYears = 400}

 120:              Debug.Print("F3")

 121:              Yield New Galaxy With {.Name = "Pinwheel", .MegaLightYears = 25}

 122:              Debug.Print("F4")

 123:              Yield New Galaxy With {.Name = "Milky Way", .MegaLightYears = 0}

 124:              Debug.Print("F5")

 125:              Yield New Galaxy With {.Name = "Andromeda", .MegaLightYears = 3}

 126:              Debug.Print("F6")

 127:          End Get

 128:      End Property

 129:  End Class

 130:   

 131:  Public Class Galaxy

 132:      Public Sub New()

 133:          Debug.Print("F1")

 134:      End Sub

 135:      Public Property Name As String

 136:      Public Property MegaLightYears As Integer

 137:  End Class