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Why Code Snippets Are Not My Cup of Tea

But how about a few good refactoring options in the Visual Studio menu

I can see another comparison between the files buried inside the HaveSameContent method. The function starts by comparing the file size. This code can be extracted to a separate method. You can make this method public, so the class can be used for file size comparison. An extracted method looks like this:

Public Function HaveSameLength() As Boolean
Return file1Info.Length = _
file2Info.Length
End Function

It’s time to remove all unnecessary comments from the HaveSameContent method. Also, since we have established that an actual, byte-by-byte comparison is only performed on files of the same size, you can simplify the condition in the While statement. It is enough to check that either byte1 or byte2 is greater than 0.

After these modifications, the HaveSameLength method looks like Listing 3. This code is actually a bit easier to read. This helps me realize one important fact, which has to do with one border condition. If the length of both files is zero, the method will return the result “False”. Now, we might argue about how we understand content equality, but I think that the majority would expect this function to return a result of “True” if both files are zero length. In my judgment, this constitutes a bug.

Had I written this code from zero, I would have probably written the appropriate unit tests. Then there would be a better chance for this border condition to be tested and for this bug to be discovered in time.

To fix this, you can introduce a guard clause. It means you will test for a special condition at the beginning of the method. If both files are zero length, exit the method right away while returning the result “True”.

While you’re at it, it makes sense to test for another special condition. Nothing prevents a client from sending the same string as the first and second file. This means that two files, file1 and file2, are actually the same physical file. For example:

If New Files(“C:/file1.txt”, “C:/file1.txt”).HaveSameContent() Then ...

In this case, if you try to execute the comparison with the original snippet code, you will end up with System.IO.IOException: {“The process cannot access the file ‘C:\file1.txt’ because it is being used by another process.”}, since the algorithm used is accessing both files simultaneously. Since the two paths in our example point to the same physical file, IOException is produced when an attempt is made to open the second file; the file is already taken. The solution is to treat this as another special case. Again, we can argue about what file equality means, but as in the previous case, I think that most of us would expect the HaveSameContent method to return the result “True” if both files are one and the same physical file and not to throw IOException.

Listing 4 provides the complete code of a Files class. Not only have you simplified and corrected the original method, you managed to structure it in a more object-oriented manner. By declaring file1Info and file2Info as fields in a Files class, you made them accessible to all class members and have managed to avoid passing them as parameters to all of the newly created methods. Only this fact, however, might not convince you that organizing the code in the form of a class was justified.

The HaveSameContent method will compare two files byte-by-byte. This is suitable for comparing binary files. However, some other file types, like text or XML files, might have different comparison semantics. In the case of XML files, the files can be considered equal even if they are not equal to the last byte. For example, two XML files might have different comments, white space, or node order, but will still produce the same output when parsed. If you need to implement XML file comparison functionality, some of the methods you already implemented in the Files class can come in handy. While a difference in length does not result in inequality between two XML files, other preconditions expressed in the methods OnlyOneZeroLength, AreBothZeroLength and PointToSamePhysicalFile apply here as well. The easiest way to implement an XML file comparison is to create a new XmlFiles class that will inherit a Files class and override the HaveSameContent method. Before that, however, the HaveSameContent method must be marked as “Overrideable” and the OnlyOneZeroLength, AreBothZeroLength and PointToSamePhysicalFile method visibility changed from Private to Protected. The code for both classes will look something like Listing 5.

I’m not suggesting you should implement XmlFiles before you even have a use for it. However, a correctly structured Files class will make implementing XML files or another file comparison class like XmlFiles, TextFiles, etc., a lot easier, once you do need it.

I think this wraps it up for the example. I hope that was enough to explain my position. To summarize, let me recap the effects that Code Snippets can have on your code and development process that make me not so enthusiastic about this Visual Studio feature:

  • Code Snippets can lead to duplicated code inside your source code.
  • Code Snippets can promote a copy-paste style of reuse.
  • Code contained in code snippets can not be unit-tested inside the Code Snippet tool.
  • As we have seen earlier in this article, code that comes with code snippets is sometimes not on the same quality level as, for example, .NET API code.

I would trade the Code Snippets feature for a few good refactoring options in the Visual Studio menu without a second thought.

More Stories By Danijel Arsenovski

Danijel Arsenovski is a software developer from Santiago, Chile. He works as a Product and Solutions Architect at Excelsys S.A, designing Internet banking solutions for numerous clients in the region. He started experimenting with refactoring while overhauling a huge banking system, and he hasn't lost interest in refactoring ever since. He pioneered the use of refactoring as a vehicle for a VB 6 code upgrade to VB .NET. Danijel is the author of "Professional Refactoring in Visual Basic" published by Wrox, and is a contributing author for several major publications. He holds a Microsoft Certified Solution Developer (MCSD) certification and was named Visual Basic MVP in 2005. He blogs at http://blog.vbrefactoring.com.

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