(this is related to this other question)
If you define an Interface where there is a Property with only a getter (= ReadOnly in VB.NET), why can you define the setter in implementing classes with C# but not with VB ?
I would have thought it was defined at .NET level, and not language-specific.
Example: for this interface
'VB.NET
Interface SomeInterface
'the interface only say that implementers must provide a value for reading
ReadOnly Property PublicProperty As String
End Interface
or
//C# code
interface IPublicProperty
{
string PublicProperty { get; }
}
This is a correct implementation in C# :
public class Implementer:IPublicProperty
{
private string _publicProperty;
public string PublicProperty
{
get
{
return _publicProperty;
}
set
{
_publicProperty = value;
}
}
}
But this is invalid in VB.NET
Public Property PublicProperty As String Implements SomeInterface.PublicProperty
Get
Return _myProperty
End Get
Set(ByVal value As String)
_myProperty = value
End Set
End Property
UPDATE 2015/04/23
Turns out this feature is coming as part of VB14 ! See Languages features in C# 6 and VB 14 and New Language Features in Visual Basic 14 :
ReadOnly interface properties can be implemented by ReadWrite props This cleans up a quirky corner of the language. Look at this example:
Interface I ReadOnly Property P As Integer End Interface Class C : Implements I Public Property P As Integer Implements I.P End Class
Previously, if you were implementing the ReadOnly property I.P, then you had to implement it with a ReadOnly property as well. Now that restriction has been relaxed: you can implement it with a read/write property if you want. This example happens to implement it with a read/write autoprop, but you can also use a property with getter and setter.
In .net, it is necessary that an implementation of a read-only property in an interface include a getter but no setter, and for the implementation of a read-write property to include both a getter and a setter. It is also necessary for the implementation of a write-only property (if one defines such a thing) to include a setter but no getter.
In C#, if a class defines a public property with the same name as a property in an interface, the public property implements the methods required by that interface, and the class does not explicitly implement the interface property, the compiler will automatically generate a property which uses the getter and/or setter of the public property, as appropriate. Even if a class implements three interfaces, one with a read-only property
Foo
, one with a write-only propertyFoo
, and one with a read-write propertyFoo
, a single public read-write propertyFoo
can be used to implement theFoo
property for all of them.Conceptually, there's no reason vb.net couldn't offer a similar feature, and generate two (or even three) different properties as required to implement interfaces. At least at present, if a vb.net class member is marked as implementing an interface member, the expectation is that it will match the member perfectly without wrapping.
Be careful assuming that VB.NET and C# are the same language spoken with a different accent - they're not.
Because VB.NET requires implementation of an interface member to have that
Implements
clause, saying which member it is implementing. C# lets you implement interface members explicitly (SORT OF like VB.NET), or implicitly (no VB.NET equivalent). Therefore the actual C# version of this isand this does gives an error: