SHORT ANSWEAR: there is no way to prevent this
Maybe this question is duplicated, but I didnt find any solutions because I dont know what words should I search for:
Option Strict On
Option Explicit On
Public Class Fruit
'... stuff
End Class
Public Class Apple
Inherits Fruit
'... stuff
End Class
Public Class FruitCart
Private _fruits As New List(Of Fruit)
Public Function GetFirstApple() As Apple
Return Me._fruits(0) '... <-- Option Strict error
End Function
Public Function GetApples() As List(Of Apple)
Dim result As New List(Of Apple)
For Each A As Apple In Me._fruits '... Why no error?
result.Add(A)
Next
Return result
End Function
End Class
The method GetFirstApple() gives me a compile error. This is the behavior I want.
The method GetApples() dont give me a compile error, leading to run-time error.
Why the compiler allows the casting on the For Each, even with Option Strict On?
I want the compiler to give me a compile error on the GetApples() method.
I just found it out. There is no way to prevent this, as documented on the "Narrowing conversions" on the For Each page: For Each documentation
Related
In VBA, is there any known mechanism to fool the compiler into allowing the use of reserved keywords as names for class properties? For example, I would like to create a property called Select in one of my class modules. However, the compiler flags my declaration as an error. Below is the syntax I used:
Public Property Get Select() As Database.SQLStatements
End Property
Database is my VBA project name and SQLStatements is one of the class modules I created. Also, I'm running the code in MS Access 2010.
You can do that and use any keyword/reserved word in your VBA. But then it will make your code a lot messy and very hard to read/debug/maintain.
If you have a bool property named If in your class you will end up with something like this If .If Then, well, good luck reading that. Also code maintenance like Find/Replace/rename etc. will need extra caution and more work.
Anyhow, if you are willing to go through all this pain, here is how you do it.
After the keywords/reserved words add a invisible blank space using ALT+0160 and that's it. VBA will consider it a perfectly legal name. e.g. If .
Also, you will have to either use intellisense for using these propertynames or manually type the altcode everywhere. That's extra typing.
clsTest
Option Explicit
Private m_sSelect As String
Private m_bIF As Boolean
Public Property Get Select () As String '~~> Select () is actually typed as SelectALT+0160()
Select = m_sSelect
End Property
Public Property Let Select (ByVal sNewValue As String)
m_sSelect = sNewValue
End Property
Public Property Get If () As Boolean
If = m_bIF
End Property
Public Property Let If (ByVal bNewValue As Boolean)
m_bIF = bNewValue
End Property
Test Module
Option Explicit
Sub demo()
Dim objTestClass As clsTest
Set objTestClass = New clsTest
With objTestClass
.Select = "It works. But it will, for sure, create readibility/maintenance issues."
.If = False
End With
MsgBox objTestClass.Select
'/ See how hard it will to read/debug this sort of code
With objTestClass
If .If Then '~~> This line here :)
MsgBox "If prop value is TRUE"
Else
MsgBox "If prop value is FALSE"
End If
End With
End Sub
ALT+0160 <> Space
I have a simple question.
Is there a difference between a one-line ReadOnly Property and a ReadOnly Property with an explicit Get Statement?
For example, In Visual Studio 2010 I used to have to do this:
Private _Message As String = ""
Public ReadOnly Property Message As String
Get
Return _Message
End Get
End Property
Public Sub New(Message As String)
_Message = Message
End Sub
But now here I am in Visual Studio 2015 and it let's me get away with this:
Public ReadOnly Property Message As String
Public Sub New(Message As String)
Me.Message = Message
End Sub
Now I wasn't trying to me lazy, I just ran across it, expecting IntelliSense to force the Get Statement. So I'm left wondering if there is a difference that I should be aware of. Is it bad practice or does it do something different?
I've managed to find tons of topics and forums about ReadOnly in C#, but I seem to be coming up dry when searching the topic regarding vb.net.
I'll appreciate any input.
Thanks! =)
Properties without explicit getters and setters are simply a syntactic convenience. There's no difference in implementation. You should generally use the second option because it makes your code more readable. Only use the first option if you need extra functionality in the getter.
The accepted answer appears to be untrue, at least for me in Visual Studio 2022.
When a property is not a constant, you have to use the multiline declaration otherwise the initial value is cached
This
Private ReadOnly Property ConnectionFile As String
Get
Return gsapppath & "\connection.txt"
End Get
End Property
returns the correct path whereas this
Private ReadOnly Property ConnectionFile As String = gsapppath & "\connection.txt"
did not include the path because the variable gsapppath was not initialized at the time the class was created, yet it was initialized at the time the property was fetched.
So it's not just a syntactic convenience, there is a functional difference.
I've had problems with default properties in my code that I can - at least to some extent - reproduce with the following code:
Public Class Dawg
Public Enum DawgEnum
Demo1
Demo2
End Enum
Default Public Property DawgProp(x As DawgEnum) As String
Get
Return "whatever"
End Get
Set(value As String)
'...
End Set
End Property
Public Sub DawgSub()
Me(DawgEnum.Demo1) = "Intellisense works here..."
End Sub
End Class
Public Class DawgTest
Public Sub SomeSub()
Dim d As New Dawg
d(Dawg.DawgEnum.Demo1) = "And here as well..."
End Sub
Public Shared Sub AnotherSub()
Dim d As New Dawg
d(Dawg.DawgEnum.Demo1) = "No help for finding 'Dawg.DawgEnum.Demo1' here..."
d.DawgProp(Dawg.DawgEnum.Demo1) = "...Intellisense helped here..."
End Sub
End Class
The problem being that within the "Shared Sub AnotherSub" when I start typing "d(" Intellisense does not offer me the list of available Enum values for the property.
I also have the problem in other classes that structurally are identical to the class "DawgTest" (a simple public class) where it doesn't work either (within a shared sub or not) - although there are no problems in the test above.
Of course, this isn't a major problem since the code compiles fine and I can always use the explicit property, but it's very annoying and confusing and just like to know, if this is by-design? And, if so: why? If not: how can I fix it?
I can't for sure say, if this problem has been there all along or, if it just came up out of nowhere...
Any thoughts - even 5 cents or less - on the issue would be greatly appreciated :o)
How can I mock one method with RhinoMocks in VB.Net? The reference I found is in C#:
Expect.Call(delegate{list.Add(0);}).IgnoreArguments()
.Do((Action<int>)delegate(int item) {
if (item < 0) throw new ArgumentOutOfRangeException();
});
SharpDevelop converts this to:
Expect.Call(Function() Do
list.Add(0)
End Function).IgnoreArguments().Do(DirectCast(Function(item As Integer) Do
If item < 0 Then
Throw New ArgumentOutOfRangeException()
End If
End Function, Action(Of Integer)))
But that doesn't work either (it doesn't compile).
This is what I want to do: create a new object and call a method which sets some properties of that method. In real-life this method, will populate the properties with values found in the database. In test, I would like to mock this method with a custom method/delegate so that I can set the properties myself (without going to the database).
In pseudo-code, this is what I'm trying to do:
Dim _lookup As LookUp = MockRepository.GenerateMock(Of LookUp)()
_luvalue.Expect(Function(l As LookUp) l.GetLookUpByName("test")).Do(Function(l As LookUp) l.Property = "value")
Unfortunately you're attempting to do both a Sub lambda and a Statement Lambda. Neither are supported in VS2008 (but will be in the upcoming version of VS). Here is the expanded version that will work for VB
I'm guessing at the type of m_list
Class MockHelper
Dim m_list as new List(Of Object)
Public Sub New()
Expect(AddressOf CallHelper).IgnoreArguments().Do(AddressOf Do Hepler)
End Sub
Private Sub CallHelper()
m_list.Add(0)
End Sub
Private Sub DoHelper(ByVal item as Integer)
if item < 0 Then
Throw New ArgumentOutOfRangeException
End If
End Sub
End Class
I have never mocked something w/ both a delegate and a lambda so I can't give a full solution to this problem, but I did want to share some example code for the usual "AssertWasCalled" function in Rhino Mocks 3.5 for vb developers because I spent some time trying to grok this... (keep in mind the below is kept simple for brevity)
This is the method under test - might be found inside a service class for the user object
Public Sub DeleteUserByID(ByVal id As Integer) Implements Interfaces.IUserService.DeleteUserByID
mRepository.DeleteUserByID(id)
End Sub
This is the interactive test to assert the repository method gets called
<TestMethod()> _
Public Sub Should_Call_Into_Repository_For_DeleteProjectById()
Dim Repository As IUserRepository = MockRepository.GenerateStub(Of IUserRepository)()
Dim Service As IUserService = New UserService(Repository)
Service.DeleteUserByID(Nothing)
Repository.AssertWasCalled(Function(x) Wrap_DeleteUserByID(x))
End Sub
This is the wrap function used to ensure this works w/ vb
Function Wrap_DeleteUserByID(ByVal Repository As IUserRepository) As Object
Repository.DeleteUserByID(Nothing)
Return Nothing
End Function
I found this to be a very nasty solution, but if it helps someone w/ the same issues I had it was worth the time it took to post this ;)
I am a vb.net newbie, so please bear with me. Is it possible to create properties (or attributes) for a class in visual basic (I am using Visual Basic 2005) ? All web searches for metaprogramming led me nowhere. Here is an example to clarify what I mean.
public class GenericProps
public sub new()
' ???
end sub
public sub addProp(byval propname as string)
' ???
end sub
end class
sub main()
dim gp as GenericProps = New GenericProps()
gp.addProp("foo")
gp.foo = "Bar" ' we can assume the type of the property as string for now
console.writeln("New property = " & gp.foo)
end sub
So is it possible to define the function addProp ?
Thanks!
Amit
It's not possible to modify a class at runtime with new properties1. VB.Net is a static language in the sense that it cannot modify it's defined classes at runtime. You can simulate what you're looking for though with a property bag.
Class Foo
Private _map as New Dictionary(Of String, Object)
Public Sub AddProperty(name as String, value as Object)
_map(name) = value
End Sub
Public Function GetProperty(name as String) as Object
return _map(name)
End Function
End Class
It doesn't allow direct access in the form of myFoo.Bar but you can call myFoo.GetProperty("Bar").
1 I believe it may be possible with the profiling APIs but it's likely not what you're looking for.
Came across this wondering the same thing for Visual Basic 2008.
The property bag will do me for now until I can migrate to Visual Basic 2010:
http://blogs.msdn.com/vbteam/archive/2010/01/20/fun-with-dynamic-objects-doug-rothaus.aspx
No - that's not possible. You'd need a Ruby like "method_missing" to handle the unknown .Foo call. I believe C# 4 promises to offer something along these lines.