LINQ and Option Strict when using custom object

Question

I use the VS10 express to compile the example in help at the below adress ...

http://127.0.0.1:47873/help/1-6644/ms.help?method=page&id=C318B79A-FA4D-4DE3-B62D-C1162BEB267E&product=VS&productVersion=100&topicVersion=100&locale=EN-US&topicLocale=EN-US

and i get the following error
Error 1 Option Strict On disallows implicit conversions from 'Object' to 'ConsoleApplication1.Module1.Student'. C:\Users\LSB\AppData\Local\Temporary Projects\ConsoleApplication1\Module1.vb 34 80 ConsoleApplication1

Any ideas?

Here is the code of the MS console example...

Imports System.Collections
Imports System.Linq

Module Module1

    Public Class Student
        Public Property FirstName As String
        Public Property LastName As String
        Public Property Scores As Integer()
    End Class

    Sub Main()

        Dim student1 As New Student With {.FirstName = "Svetlana",
                                     .LastName = "Omelchenko",
                                     .Scores = New Integer() {98, 92, 81, 60}}
        Dim student2 As New Student With {.FirstName = "Claire",
                                    .LastName = "O'Donnell",
                                    .Scores = New Integer() {75, 84, 91, 39}}
        Dim student3 As New Student With {.FirstName = "Cesar",
                                    .LastName = "Garcia",
                                    .Scores = New Integer() {97, 89, 85, 82}}
        Dim student4 As New Student With {.FirstName = "Sven",
                                    .LastName = "Mortensen",
                                    .Scores = New Integer() {88, 94, 65, 91}}

        Dim arrList As New ArrayList()
        arrList.Add(student1)
        arrList.Add(student2)
        arrList.Add(student3)
        arrList.Add(student4)

        ' Use an explicit type for non-generic collections
        Dim query as system.collections..Generic.IEnumerable(Of Student) = From student As Student In arrList
                    Where student.Scores(0) > 95
                    Select student

        For Each student As Student In query
            Console.WriteLine(student.LastName & ": " & student.Scores(0))
        Next
        ' Keep the console window open in debug mode.
        Console.WriteLine("Press any key to exit.")
        Console.ReadKey()
    End Sub

Try the above example using Console and Option Strict

Answer 1

you can cast but a little bit cumbersome as the generic list is the solution since version 2005 for this which extended the arraylist

Use

Dim students as List(0f student) instead as Dim arrList as new ArrayList()

The studends List keeps than a strongly typed arraylist of students.

 

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Success
Cor

Answer 2

I would just replace the arrList with:

Dim studentList = New List(Of Student) From {student1, student2, student3, student4}

 

The trouble with ArrayList objects are that they are not type-safe.  Option strict is giving a compile time error for something that could easily turn into a run-time error.  I imagine the code will run, but if the arrList object contains anything other than a student type it will blow up...

 

I also prefer the method syntax over the query syntax.....but that is personal preference:

 

Dim result = studentList.Where(Function(x) x.Scores.Where(Function(y) y > 95).Any()).ToList()

Answer 3

you can cast but a little bit cumbersome as the generic list is the solution since version 2005 for this which extended the arraylist

Use

Dim students as List(0f student) instead as Dim arrList as new ArrayList()

The studends List keeps than a strongly typed arraylist of students.

 

---

Success
Cor

Hi Cor,

Better to add a NEW in there.

Dim students As New List(Of Student)

 

to avoid an exception error.

;-)

 

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Regards,

John

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