Question

I currently use string literals in my xpath expressions. For example:

paragraphList = root.SelectNodes("paragraph");

I know you should generally avoid using literal values, but I figure this is safe, since the names of your xml nodes will rarely change. Is this bad practice, or am I same?

Answer 1

Well, the principle behind the concept of avoiding literals is maintainability. So ask yourself what the maintainability ramifications of each decision are.

In this case, changing from

paragraphList = root.SelectNodes("paragraph");

to

paragraphList = root.SelectNodes(PARAGRAPH_TAG);

doesn t seem to introduce a readability issue. So the question comes down to laziness and how many places you use each string literal.

What I d probably do (assuming it s only you touching the code) is go ahead and use string literals initially, but as soon as you have a second usage of any given string turn it into a constant.

Then again, if you are using the ReSharper plugin to Visual Studio, you can use the "Introduce field" refactoring with a simple key combination, so the laziness doesn t weigh quite so much :-)

Answer 2

My general rule of thumb is to NEVER use string literals. I think there are many benefits to not using string literals, a couple of which were already mentioned by Benjamin Cox.

Centralization: If all your string literals are replaced by static string constants (ideally all grouped together in one place, perhaps at the file level), then you know exactly where to find all your string references. Plus some compilers offer convenient functions like "Jump to Definition" to access them faster.
Maintainability: As a result of 1, it s easy to see that, should the need arise, you can change string references in one place and have those changed immediately reflected throughout your code.
Efficiency: Memory is only allocated once for each unique string reference you create, so you aren t constantly allocating new strings into memory like you do when you use the same string literal all over the place. (Some languages, like Ruby, can automatically handle this case by encouraging the use of symbols instead of strings.)
Readability: Especially if your string literals are a little cryptic, it s easier to read an appropriately named static variable: kCapturedImageDirectoryFormat as opposed to "capture-%.0f.tmp"

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