[PATCH] Air isn't special

[Henrik Brautaset Aronsen]

Linus Torvalds wrote:
>
>
> On Jun 1, 2014 9:05 AM, "Dirk Hohndel" <dirk at hohndel.org 
> <mailto:dirk at hohndel.org>> wrote:
> >
> > I know that eventually Linus will chime in. There were a number of good
> > reasons why we did this incredibly annoying thing. And every time I 
> decide
> > to say "to hell with Linus" and change it, he has a very good reason why
> > that's a really dumb idea.
>
> Air really *is* special.
>
> And it's a lot easier to just use "get_o2()" than to fight that 
> fundamental fact.
>
> Anybody who thinks air is just the same as nitrox with 21% o2 is out 
> to f*cking lunch. That may be true from a physics standpoint, but it 
> is not true in any other way.
>
> Air is special because you have to check against both 21 and 20.9.
>
> Air is special because it also is "uninteresting" for both loading and 
> saving.
>
> Air is special because it's also "empty" as far as cylinder contents 
> go (and anybody who says that people should just write 21% to mark the 
> cylinder in use has his head so far up his ass that it's dark in there).
>
> In other words, air IS SPECIAL.
>
> Not making air special is a mistake. You'll end up having to add all 
> those "air is special" tests to various random places, and you'll 
> forget some of them. And when you forget one of them, you'll have 
> really subtle bugs, that are annoying and hard to find.
>
> In contrast, of you'd just admit that air is special, all this goes 
> away. Use "get_o2()" and be happy. You'll never have to think about 
> all the special cases, and if you miss a get_o2() the big well be 
> obvious and clear.
>
> Really. It is that simple. Air really is special. Don't try to make it 
> be just another form of nitrox, you're *wrong*.
>

I heartily disagree.  The only places we need to treat air specially is:

- when we read dives from a file.  then we should do the right thing and 
set the correct gas fractions from the start.
- when we save dives to a file.  (if we want to not print o2=20.9, that 
is.  and we probably do)
- when we want do display air as the text "air" in the gui

That's it.  It's not wrong at all.

Henrik

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