Wednesday, September 19, 2012

Don't "Namespace" Filenames

When I first started this blog, I wrote up a rant about directory names that mislead about what their contents are. At the same time, I complained about adding unnecessary morphemes to directory names, things like "db" or "model" or such-like.

I've recently become annoyed with the habit of -- for want of a better term -- "namespacing" directory names and file names. I'm not saying not to use good namespace discipline in source code. What I mean is having a directory structure like this:

  zoo/
    zoo_iface/
      zoo_cmds.hpp
      zoo_cmds.cpp
      ...
    zoo_model/
      zoo_cage.hpp
      zoo_animal.hpp
      ...

Why does everything have to start with "zoo"? Look at it this way: if that was how we named people, then everyone's last name would be part of their first name and also part of their middle name. Instead of calling someone Mary Jane Smith, we would know her as MarySmith JaneSmith Smith. Some people make it even worse by prepending the full directory name onto the file name -- like "zoo_model_cage.hpp". Poor Mary Jane would be MaryJaneSmith JaneSmith Smith.

Of course, a source file name may be dictated by its contents -- you're following our C++ standard, right? -- so my ire is directed at redundant directory names more than filenames.

This principle doesn't have to stop at source files.  It boggles my mind that raw bug testcases where I work start their life with names like this:

  /home/bugs/prod1_bugs/comp2_bugs/bug6003.tgz


For crying out loud, I know this is a directory full of bugs, can't we just call each bug something like:

  /home/bugs/prod1/comp2/6003.tgz


?


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Tuesday, September 11, 2012

Disabling Auto-Indent in Emacs

I have to edit a C++ file at work whose indentation is so screwed up that any punctuation key I type ends up changing the indentation of the line I'm working on to something that is way out of line with the text right around it. For sanity's sake I have to M-x set-variable c-syntactic-indentation nil when I'm working on that file. The c-syntactic-indentation variable does not start out buffer-local, meaning that for the sake of the one stupid file, I have turned off the very useful feature of syntactic indentation for every file I have open in that session. So, if you are ever going to set it temporarily, make sure you have this line in your .emacs file:

  (make-variable-buffer-local 'c-syntactic-indentation)
 
While you're at it, don't you want a shortcut for the set-variable? I amused myself greatly this morning as I tried to think what shortcut I would assign this action to. The obvious mnemonics I polled with C-h k were taken: I have C-c TAB set to indent-region, C-c ; to comment-region, and C-c { set to a function to insert a skeleton class definition.  What to do?  I finally hit upon C-c (, and lo-and-behold I had already set that keystroke to toggle c-syntactic-indentation, sometime in the distant past! Here's the code:

  (global-set-key "\C-c("
                  '(lambda ()
                     (interactive)
                     (setq c-syntactic-indentation (not c-syntactic-indentation))
                     (message "c-syntactic-indentation set to %s"
                              (if c-syntactic-indentation "t" "nil"))))


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Friday, June 1, 2012

Emacs: Scroll Other Window Up

It often happens that I have two related files open in one emacs frame, and I want to scroll around comparing them.  Of course to scroll back and forth in a single buffer, C-v scrolls you down, and M-v scrolls you up. (In a perverse bit of emacs jargon, C-v's function is called "scroll-up", since the text moves "up" relative to the fixed window -- even though every human wanting to look lower in the file thinks and says "scroll down, scroll down" -- and M-v's function is called "scroll-down".)

To keep two files synchronized as you peruse them, the power tool to use is M-x ediff-buffers, which sets up an interactive diff session to step through the diffs. Within ediff, a simple lowercase "v" scrolls lower in both files at once, and uppercase "V" scrolls higher. Don't forget M-x ediff-revision as a handy tool for comparing a version-controlled file to its latest revision, or for comparing two different revisions interactively.

Ediff is great, but sometimes it is too heavy-handed for the eyeballing I'm trying to do. For one thing, if one of the files contains a large section that is missing in the other, scrolling both files at once means striding through the section in one window while inching down a line at a time in the file that lacks it. Also, navigating ediff can be tedious if there are a great number of changes or reordered chunks, and once your diffs no longer line up sensibly, ediff's highlighting is simply a nuisance.

So there are the old standbys C-v and M-v, plus there is the handy M-C-v, which scrolls lower in the other window. That is, if I have a.txt and b.txt open in a single frame, and the cursor is in a.txt, then M-C-v will show a lower chunk of b.txt, to keep up with C-v in a.txt. Until today, whenever I wanted to move higher in b.txt, I didn't know of a single keystroke to do that, so I always just switched windows and used M-v. I could do C-u - M-C-v, but I never liked that.

Turns out there is a keystroke to scroll higher in b.txt without switching windows: M-C-S-v -- same keys as scrolling lower, plus the shift key. Now, M-C-v is a pretty ergonomic companion to C-v. I lean the base of my left hand on the Ctrl key, hit V with my left index finger, and keep my thumb poised over the Alt key to choose which window to scroll. The shift key just does not fit in with this scheme. With some effort, I can hold it with my left pinkie, but it's not comfortable. So my new solution is to tie that command to C-c M-C-v. True, it's not a single keystroke, but unlike the C-u solution above, it's all in the left hand, and close together without being cramped. The .emacs line is:

  (global-set-key "\C-c\M-\C-v" `scroll-other-window-down)

Yes, the command to go higher in the file -- to scroll up as we humans say -- is "scroll-other-window-down".


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Thursday, January 12, 2012

gcc error: invalid use of member (did you forget the `&' ?)

Every time I have gotten the above compilation error, it has nothing to do with a missing ampersand. Instead, it is missing function-call parentheses:

  if (you_go && use->yourMember) { // WRONG!
    this->isInvalid();
  }

  if (i_go && use->myMember()) { // Oh yeah, the parens.
    continue;
  }

So don't use your member invalidly.


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