Named namespace in implementation file to group const string literals - Good/Bad?

Question

I've grouped several message strings into a named (non anonymous) namespace in the .cpp file for a class handling output as seen in the code below:

namespace Messages
{
  static const std::string AppTitle = "The Widgetizer - Serving all your Widget needs";
  static const std::string SuccessMsg = "Great success! Widgets for all! ";
  static const std::string FailMsg = "No widgets for you!";
};

void Display::printTitle()
{
  out << Messages::AppTitle << std::endl;
}

void Display::printSuccessMsg()
{
  out << Messages::SuccessMsg << std::endl;
}

void Display::printFailMsg()
{
  out << Messages::FailMsg << std::endl;
}

My logic being that this way they're all in one central location, under a namespace with a meaningful and self-documenting name, and they're not exposed to the client code (as they would be if I had put the namespace in the .h file).

Is this a good practice generally or are there pitfalls to this that I'm not seeing?

Is the static keyword necessary if they're in a file scope namespace like this?

In terms of best practices and accepted C++ idiom & style, would this be better off just as an anonymous namespace? Or simply as static const class members?

I admit it's probably overkill for the small program I'm writing since they'll probably only be used in these functions but generally speaking not hard coding message strings is a good habit no?

Answer 1

It's okay I guess, you won't lose any points for this. I don't care much for the term "best practice", it is not a common practice. A lot of programs are written with localization in mind, there's several billion potential customers that don't understand a word of English. No standard C++ solution for that, just common practices on your platform. Like string resources.

Answer 2

Is this a good practice generally or are there pitfalls to this that I'm not seeing?

It don't seem to be any problem with using namespace to do this.

I often see that putting constant values and global configuration variables in namespace (might they be accessed outside of the definition cpp or not) is a good practice. That way you don't have to create a class just for grouping and you still have the name encapsulation working nice.

Is the static keyword necessary if they're in a file scope namespace like this?

It's not necessary.

In terms of best practices and accepted C++ idiom & style, would this be better off just as an anonymous namespace? Or simply as static const class members?

Static class member would be overkill and non-sense. If you don't need an instance, don't write a class.

Anonymous namespace would be useful only if the code is limited to a specific CPP file.

I admit it's probably overkill for the small program I'm writing since they'll probably only be used in these functions but generally speaking not hard coding message strings is a good habit no?

Following the DRY principle, it looks like you've done well, even for a small program and even if you think your constants will be used only once. Because in the end you never know what the future is made of.

Answer 3

This is okay if you desire the clarity.

My preference would generally be either:

1. To define file level static variables without the name space (these are always near the top of the file for me).
2. To define an anonymous namespace and use non-static variables.
3. Put the definitions in a private part of my subsystem in their own file, complete with header file.

In a particular case that I did use the method you describe it was a mistake. I had fairly large file 3000+ lines with a number of internal classes. In retrospect I should have put my scoped classes into separate files in the internal part of my subsystem.

Generally I prefer 1 or 2 for simple things and 3 for complicated/large things.

Answer 4

Is this a good practice generally or are there pitfalls to this that I'm not seeing?

Grouping related objects in a namespace is good practice if it makes the code clearer; there aren't any particular pitfalls, but deeply nested namespaces can lead to excessively verbose code if you're not careful.

Is the static keyword necessary if they're in a file scope namespace like this?

You need either static or const to give them internal linkage, but it might be better to enclose your namespace in an unnamed namespace instead. Using static at namespace scope is deprecated, and just using const means you'll get a surprise if someone declares extern objects with the same names.

In terms of best practices and accepted C++ idiom & style, would this be better off just as an anonymous namespace? Or simply as static const class members?

If grouping them in a named namespace makes the code more expressive, then do it; otherwise, don't. I'd prefer not to make them class members unless necessary, to avoid adding unnecessary declarations to the header file.