Hello world!
Using the following code:
Function GetSetting(Of T)(ByVal SettingName As String, ByRef DefaultVal As T) As T
Return If(Configuration.ContainsKey(SettingName), CType(Configuration(SettingName), T), DefaultVal)
End Function
Yields the following error:
Value of type 'String' cannot be converted to 'T'.
Any way I could specify that in all cases, the conversion will indeed be possible (I'm basically getting integers, booleans, doubles and strings).
Edit: There seem to be three solutions now:
- Using the `ValueAs` function provided by AMissico
- Casting to an `object`, then to `T`, with a check for null values
- Using a `DirectCast` over Convert.ChangeType
Which would you suggest?
Edit 2: Would this code work?
Function GetSetting(Of T)(ByVal SettingName As String, Optional ByRef DefaultVal As T = Nothing) As T
Return If(Configuration.ContainsKey(SettingName), ConvertTo(Of T)(Configuration(SettingName)), DefaultVal)
End Function
Function ConvertTo(Of T)(ByVal Str As String) As T
Return If(Str Is Nothing Or Str = "", Nothing, CType(CObj(Str), T))
End Function
Edit 3: [AMJ] Working Code
Function GetSetting(Of T)(ByVal SettingName As String) As T
Return GetSetting(Of T)(SettingName, Nothing)
End Function
Function GetSetting(Of T)(ByVal SettingName As String, ByVal DefaultVal As T) As T
Dim sValue As String = Configuration(SettingName)
If Len(sValue) = 0 Then
Return DefaultVal
Else
Return CType(CObj(sValue), T)
End If
End Function
Quick Test Method
Public Sub DoIt()
Me.Configuration.Add("KeyN", Nothing)
Me.Configuration.Add("KeyE", String.Empty) '""
Me.Configuration.Add("Key1", "99")
Me.Configuration.Add("Key2", "1/1/2000")
Me.Configuration.Add("Key3", "True")
Me.Configuration.Add("Key4", "0")
Dim o As Object 'using object in order to see what type is returned by methods
o = Value(Of Integer)("KeyN", 10) '10
o = Value(Of Integer)("KeyE", 10) '10
o = Value(Of Integer)("Key1", 10) '99
o = Value(Of Date)("KeyN", #11/11/2010#)
o = Value(Of Date)("KeyE", #11/11/2010#)
o = Value(Of Date)("Key2", #11/11/2010#)
o = GetSetting(Of Integer)("KeyN", 10) '10
o = GetSetting(Of Integer)("KeyE", 10) '10
o = GetSetting(Of Integer)("Key1", 10) '99
o = GetSetting(Of Date)("KeyN", #11/11/2010#)
o = GetSetting(Of Date)("KeyE", #11/11/2010#)
o = GetSetting(Of Date)("Key2", #11/11/2010#)
Stop
End Sub