Some code samples in WROX books are bad.

[mangel]

When I pay $60 for a book on VB .NET or any other programming language in Visual Studio, I expect the code supplied to work when both the Option Explicit and Option Strict are set to TRUE. At the very least Option Explicit should be set to TRUE. It is bad practice to write any program where these are set to FALSE. WROX books should not be teaching bad coding practices. WROX needs to have a policy consistent with this and it needs to communicate this requirement vigorously to their authors. I wasted a lot of time trying to figure out what kind of an object "item" is. Declaring it as an "object" only sets up a late binding condition when one isn't necessary. Learning the "item" object type is part of what the reader needs to learn; this is a situation that WROX books need to avoid.

It would be useful to hear what other readers think about this issue.

[jminatel]

Can you tell us what book, what chapter this is about?

[mangel]

Originally Posted by jminatel

Can you tell us what book, what chapter this is about?

The book is "Professional Visual Basic 2010 and .NET 4", Chapter 10 "ADO .NET and LINQ", page 424. There are two issues: one is fixed in the explanation right after but I didn't know that and so I wasted a lot of time trying to type in the code without errors.

The second issue is the undefined variable "item" which should have been followed by "As title"; this is not fixed in the explanation.

The author should also alert the reader to references and imports that are necessary for the code to work. This is done in the explanation that follows but it would have saved a lot if the alert is provided before the reader enters the code. It seems that authors try to add a little suspense for interest sake. But readers of computer books are not looking for suspense; they just want to learn the subject. When they want suspense, they'll read a mystery novel instead.

I would not be surprised if there are similar issues throughout the rest of the book; I went straight to Chapter 10 in order to learn about LINQ. That's why I say that good coding examples should be an enforced WROX policy.

The bottom line is that the authors of WROX books need to be more considerate of their readers, whose skill level will range all over the spectrum.

[Imar]

I don't have the book so I can only guess, but could it be that the example is using the new Type inference system? Consider this example:

 
Class Person
  Public Sub New()
  End Sub
End Class
 
Class TestApplication
  Private Sub MethodName()
    Dim somePerson = GetPerson()
  End Sub
 
  Private Function GetPerson() As Person
    Return New Person()
  End Function
End Class

Despite what it looks like, the somePerson variable *is* strongly typed as a Person and not as an Object as the compiler infers the type of the variable based on the value that is assigned to it. Since GetPerson returns a Person, the somePerson variable is typed as a Person as well with this code.

This code works with Option Explicit and Option String set to On, as long as Option Infer is On as well.

Cheers,

Imar

[Imar]

Just did some digging in the source code and indeed the example you're referring to is using type inference.

Consider this:

Dim query As Table(Of title) = dc.titles
For Each item In query
  Console.WriteLine("{0}: {1}",
     item.title_id,
     item.title)
Next

Here, item *is* a title instance and not an Object. That's why you get IntelliSense when you type item and then a dot. Additionally, you can see the type of the item variable by hovering your mouse over item in the line with For Each. You see a popup telling you that item is, in fact, a title instance.

Type inference is explained in Chapter 1, page 18 and further. Stuff like Option Explicit and Option Infer are described in detail there as well.

LINQ in .NET relies heavily on type inference, mainly because of the dynamic nature of queries and anonymous types.

So, if you want to hear "what other readers think about this issue", I'll say you're being a bit too harsh on this book and the code examples. The example you're referring to is technically correct, and shows best practices when it comes to type inference in queries. If you don't like the syntax of type inference, you can always add "As title" to the code to make it more explicit, but it's certainly not neded to write type-safe code.

Hope this helps.

Cheers,

Imar

[mangel]

Hi Imar,

I have your Beginning ASP .NET 4 etc book. Also thanks for taking the time to look at this issue.

You said that the code provided in the book of issue is:

Dim query As Table(Of title) = dc.titles
For Each item In query
Console.WriteLine("{0}: {1}",
item.title_id,
item.title)
Next

But in the book the verbiage between "query" and "=" is not there. I just think that is should have been.

The other part regarding Option Infer I was not aware of and thanks for the explanation. My difficulty was due to not starting the book with chapter one; I went straight to LINQ in chapter 10. I was basically interested in that before attempting to read a book devoted to it. However, your explanation was short and sweet and could have been provided at the beginning of the LINQ section in the book. Because Option Infer was added specifically due to LINQ, it probably should have been reviewed at the beginning of the LINQ section or at least the reader should be asked to return to chapter 1 page 18 and review the compile options.

I don't know but when you write a book for WROX, do you consider the possibility that the reader may skip ahead?

I went straight from VS2005 to VS2010, so I had never tried LINQ until now.

So perhaps I was too harsh. Perhaps I should have read the first chapter first.

Thanks,

Mangel

[Imar]

But in the book the verbiage between "query" and "=" is not there. I just think that is should have been.

You can add it there, but you don't have to. The same principle applies:

 
Dim query = dc.titles

would work fine. dc.titles is a Table(Of Titles) and thus when the compiler sees this, it types query as a Table(Of Titles). So, the code in the book should compile just fine and when you hover your mouse over query it should tell you the type.
The code in the download is slightly different and does include the As clause.

Because Option Infer was added specifically due to LINQ, it probably should have been reviewed at the beginning of the LINQ section or at least the reader should be asked to return to chapter 1 page 18 and review the compile options.

Yes, I agree. That would certainly make sense....

I don't know but when you write a book for WROX, do you consider the possibility that the reader may skip ahead?

It depends on the book I guess. My Beginning books are meant to be read from start to end. I do add forward and back references where appropriate. With a reference type of book things would be different.

I think it's a fine balance. If you need to repeat some stuff in every chapter, you may get the opposite effect where people don't like the fact the same information is repeated over and over again ;-)

But in your case, a reference in the LINQ chapter to the compiler options and an explanation of type inference would have been useful.

Cheers,

Imar