Quote:Original post by c0uchm0nster
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Err, but you see that you basically copied my post with some added salt?

The only difference being that you explicitly don't recommend to use an instance of some class that is passed through (whereas I implicitly didn't recommend that inside my code-sample).

Quote:Passing an instance of a class along to every function in your project is sloppy and not much better than globals (it could even be worse).

No, it is better than global variable, because you can limit visiblity before nodes higher in the call-tree and before nodes deeper in the call-tree. E.g., say your call-tree is [<program-scope>, <filescope>, x_0, x_1, x_2, x_3, x_4, x_5, x_6, x_7]. Then you can make it so that only [x_2..x_4] can see and use a particular instance of some class, but [<program-scope>..x_1] and [x_5..x7] can't neither. You can even make it so that only x_2 has random-access to your instance, but [x_3..x_4] only get read-access. You can even control when your instance is constructed, and when it is destructed, with global variables, you can not.


Anyways, that is not what I recommended. I recommended (I know it wasn't your idea to pass them through, just clarifying):


It's not a global variable, it's not passed through, it's not a singleton, it does not contain any static methods, and with an increasing number of paths, adding new values is even less typing work than writing redundant pairs of declarations and definitions (*). And the function main() will work fine in the future when you rewrite the exemplary class Environment to something like:



Also, you can anyhow declare a global instance of that class, if you must, and still be future safe to some degree (if you ever intend to make such paths configurable some day, you could run into static initialization order fiasco).

Btw, using a surrounding class, your code became (unclean):

Not less clear, and just one additional char. Plus, sorry, you are future safe to some degree.

Anyhow, I have nothing against globals in that case actually, but my intention was a bit blurred. Though a class doesn't cost more than a namespace, in any respect. But you get some benefits (no, YAGNI arguments are not applicable, as wee see at (*)).

Quote:Notice that the extern keyword only appears in 1 place, the .h file declaration.

It is still perfectly allowed to put the extern keyword upon definitions, which will contribute to self-documenting code (you clarify that you didn't intend to make that variable file-global, but program-global).

Quote:Notice that the variables can be const.

Actually, they should be const.


(*)
(p-code with a handful of paths)


vs.





edit
sidenote: You could also make the member functions static, or non-member inline functions.

[Edited by - phresnel on April 30, 2009 5:04:58 AM]

Quote:Original post by icecubeflower
Hey Phresnel, you define the Environment class above main(). You declare an instance of it in main() called env. Don't you have to pass env to everything that needs those paths?

You can do one of those:
0) You pass it through (maybe as const-reference, i.e. as read-only)
1) Everyone who needs the information declares an own, local instance
2) You create a global instance

Quote:
And if there's a class defined in another file, it's going to look like this:

class Whatever{  void FunctionThatNeedsPathInfo(Environment &env);};

There are two solutions:

class Environment;class Whatever{  void FunctionThatNeedsPathInfo(Environment &env);};

Which works because you pass by reference. But you will have to #include the whole definition of Environment before the actual definition "void FunctionThatNeedsPathInfo(Environment &env) { .... }".

Or, better, just #include the proper file:

#include "environment.h"class Whatever{  void FunctionThatNeedsPathInfo(Environment &env);};

Of course, environment.h was only before function main() for the sake of example. So put it into a header-file (like your extern declaration previously), but don't forget include guards (#ifdef XXX ... #define XXX ... #endif // XXX).

Quote:Were you just typing a general solution and I was supposed to figure that out or am I misunderstanding something?

Yes.
;)