C# - Compiler Does Not Do Implicit Casts To Object?
Apr 10, 2011
I've recently had a strange issue with one of my APIs reported. Essentially for some reason when used with VB code the VB compiler does not do implicit casts to Object when trying to invoke the ToString() method.The following is a minimal code example firstly in C# and secondly in VB:
Graph g = new Graph();
g.LoadFromEmbeddedResource("VDS.RDF.Configuration.configuration.ttl");
foreach (Triple t in g.Triples)[code].....
This appears to be due to the fact that the type of the property t.Subject that I am trying to write to the console has explicitly defined ToString() methods which take parameters.The VB compiler appears to expect one of these to be used and does not seem to implicitly cast to Object and use the standard Object.ToString() method whereas the C# compiler does.Is there any way around this e.g. a VB compiler option or is it best just to ensure that the type of the property (which is an interface in this example) explicitly defines an unparameterized ToString() method to ensure compatability with VB?
Graph is an implementation of an interface but that is actually irrelevant since it is the INode interface which is the type that t.Subject returns which is the issue.INode defines two overloads for ToString() both of which take parameters Yes it is a compile time error No I do not use hide-by-name, the API is all written in C# so I couldn't generate that kind of API if I wanted to
Note that I've since added an explicit unparameterized ToString() overload to the interface which has fixed the issue for VB users.
I have an error in my VB.net program - I have tried various casts etc but it just will not resolve the issue - so reluctantly I post it here to see if anyone else has a similar problem.
Error 1 Option Strict On disallows implicit conversions from 'Object' to 'String'.
Private DS As New DataSet ' Languages Function TransTxt(ByVal Frm As String, ByVal Item As String) As String
I get "Option Strict On disallows implicit conversions from 'Object' to 'ExpTreeLib.CShItem'.", which is a listview that I have on my form, which references expTreeLib.dll
I'm using a LINQ query to translate data inside a DataTable object to be a simple IEnumerable of a custom POCO object.
My LINQ query is:
Dim dtMessages As DataTable '...dtMessages is instantiated ByRef in a helper data access routine... ' Dim qry = From dr As DataRow In dtMessages.Rows
[code]....
However, the compiler is throwing a warning message under dr As DataRow with the message: Option Strict On disallows implicit conversions from 'Object' to 'System.Data.DataRow'.Why am I getting this error and what do I need to do to fix it? I would have thought that dtMessages.Rows returned a collection of type DataRow. Is this not correct?
I have written a small program to aide my business and the program works fine. But while compiling the code it shows a lot of warnings like the following."late bound resolution; run time errors may occur""implicit conversion from 'Object' to 'String'." Where am i going wrong. Even though the options strict off removes the warning I want to correct the warnings.
Private Function ledgerMasterFullName(ByVal i As Integer) As String Dim fullName As String Dim vObj As Object
Public Sub FB(OF T0 As IGH_Goo, T1 As IGH_Goo) _ (ByVal A As DataTree(Of T0), _ ByVal B As DataTree(Of T1)) Dim val_A As T1 = DirectCast(A.FirstItem, T1) End Sub
Imports System.CodeDom.Compiler Public Class iCompiler Public Shared Sub GenerateExecutable(ByVal Output As String, ByVal Source As String, ByVal Icon As String)[code].....
This error first appear to occur randomly. Steps to recreate:Open Visual Studio and load a solution (some files automatically opened) - this is when the problem occurs Close all open files Restart visual studio and load solution (no issues)Open Exactly the same files again, restart visual studio and load solution so files open automatically (problem occurs!)
However, when trying to narrow it down to a single file (that is automatically opened when the solution is loaded), I couldn't reproduce the problem. Now with all the files open again the problem doesn't occur!!! So it looks like it is fixed - though this happened before and eventually the issue came back.
I think it is to do with one of the user controls with DevExpress controls on it - when the error occurs, the designer displays the error. Though I can't reproduce it at the moment to confirm that.
If I look at the IL that is created in Linqpad for the two following code snippets, I wonder what happens here.
In c# int i = 42;
results in the following IL code
IL_0000: ret
whereas in VB
Dim i As Integer = 42
it is
IL_0000: ldc.i4.s 2A IL_0002: stloc.0
Apparently, the c# compiler understands the the value is never used and thus simply returns nothing. In VB.NET the actual code is translated.Is that due to differences in compiler optimization or is there anything else at work?
Update: Just to clarify this - I just enter this one line into LinqPad and look at the IL it creates (most definitely by running the respective compiler). There is no program.
I've frequently coded something along the lines of the sample below(with stuff like Dispose ommited for clarity. ). My question is, are the volatiles needed as shown? Or does the ManualResetEvent.Set have an implicit memory barrier as I've read Thread.Start does? Or would an explicit MemoryBarrier call be better than the volatiles? Or is it completely wrong? Also, the fact that the "implicit memory barrier behavior" in some operations is not documented as far as I've seen is quite frutrating, is there a list of these operations somewhere?
class OneUseBackgroundOp { background args[code].....
If default 'sa' account has sys_admin permissions for the whole SQL instance and all its databases. On the database itself, if I don't have db_datareader permission enabled, I would assume it doesn't need it as it is implied but I was wondering in .net, is there way to check if db_datareader has explicitly been enabled and not just implied from the 'sa' being a sys_admin.
As most of you know, .Net framework 4.0/Visual Studio 2010 supports implicit line continuation in VB, which was not available in previous versions (at least not to my knowledge). I have a situation where I am working on an ASP.Net 3.5 application that is targeting a machine that does not currently have .Net 4.0 installed and from what I understand it won't be installed for some time yet on that machine. Obviously, my development machine does have .net 4.0 installed.
With the implicit line continuation feature in VS2010, I sometimes find myself forgetting to add the continuation, and VS2010 does not have an issue with that even when I am targeting a previous version. Additionally, I know that if I actually compile the code (business objects and such), issues with line continuation are not a problem, as the compiled dll works fine as a 3.5 .net file.
My concern is this. There are areas where I am doing VB.Net coding in the code behind(beside?) for the asp.net pages. These would only be compiled on the server when they are first used, but since the server doesn't have the .net 4.0 framework (or even if it did), does anyone know if this would this cause the compilation to fail if I missed a line continuation? If so, is there a way to enforce using line continuation characters in VS2010?
I realize that some best practices might not be getting followed here, but I'm not about to change all the development dynamics around here just yet. Also, I'm not in an environment where I could easily test this out on my own.
VB 2008 Express edition. I'm pretty new to VB2008, a little over halfway through my first classi am writing a console program to ask the user for the price of gas for 7 days, then to get the average of that price. here is my code so far:
In C# you can use the implicit keyword to define an implicit user-defined type conversion operator.In VB.NET you can define a CType conversion operator that will explicitly convert a user-defined type into another type.Is there a way to declare an implicit conversion operator in VB.NET?
I have 2 methods with the same name, with diferente signatures.
Public Sub Method1(ByVal Parameter1 as String, ByVal Parameter2 as Boolean) Public Sub Method1(ByVal Parameter1 as Integer, Optional ByVal Parameter2 as Boolean = False, Optional ByVal Parameter3 as Boolean = False)
If I call Method1("My String Parameter", False) it will not give and error, it will try to convert the parameter to integer and use the overload.
Is there a way to forbid the implicit conversion in this specific method or in this specific parameter. For instance, I changed the second method name, but its not an elegant solution.
The code compiles and seems to run correctly, but is underlined with the message "Implicit Conversion from 'Double' to 'Single'" Why would this be an implicit conversion if each of the variables is cast as a Single? Is this something I should worry about or change?
VB.Net just showing its true colors again? When I turn Option Strict On, I am still able to do implicit narrowing conversions in a for each loop.For example, this code actually compiles;
Private Sub foobar() Dim foo() As foo = {New foo} For Each bar As bar In foo[code].....
From my understanding of Option Strict, this should not work.See here "Restricts implicit data type conversions to only widening conversions".My code above is a narrowing conversion, and so should be illegal.It will fail at runtime with an InvalidCastException. C# does the same thing. Below is another implicit narrowing conversion.
In C# I can create an interface, and when I use the interface the compiler knows that certain interface requirements are fulfilled by the base class. This is probably clearer with an example:
[Code]...
On all my forms, or is a better route creating an abstract base class that has SetupForm() (and how do you do that in VB.net)?
I have a C# library that internal clients configure with VB.Net Their scripts are throwing an InvalidCastException where they really shouldn't.
So the code is something like this (massively simplified):
//C#3 public class Foo { public static implicit operator Foo ( Bar input )
[Code].....
Strange - it looks like the VB.net compiler can find the cast operator but it's lost at runtime. Surely the VB and C# IL will be pretty similar here?
The VB.net code is dynamically compiled - the compile happens the first time a user logs into the app. it's being compiled as VB.Net against .Net 3.5, and I'm not using any COM interop.
Possible Duplicate: How can I create an interface in VBNet with implicit implimentations I'm normally a C# developer and completely new to VB.NET, so be nice with me.;) Let's say that I have this base class:
[Code]....
Is there any way of not having to use these "proxy"-calls to the real method? I haven't found any useful information about this in the CLI-specification, which makes me suspect that this is a VB.NET "feature". Is this the case?
