Tab indentions on different platforms?

[Ben Finney]

Steven D'Aprano <steve at REMOVE-THIS-cybersource.com.au> writes:

> On Sat, 29 Dec 2007 15:29:25 +0000, Thorsten Kampe wrote:
> 
> > I'd personally go for spaces because:
> > 
> > 1. I don't like things I cannot see (control characters)
> 
> You can see spaces but not tabs? Your editor is pretty weird. In all
> the editors I've every used, both spaces and tabs show up as empty
> white space. (Or coloured space if I set the editor to use a
> coloured background.)

Though Thorsten could have been clearer, "thing that is not a space
character but shows up as white space" is a near-enough approximation
of "thing I cannot see".

> > 2. I never had problems with spaces but plenty with tabs
> 
> Periodically, I ask on this list what problems people have with
> tabs. (I'm fully aware that mixing tabs and spaces is a Bad Thing.)
> I've had little luck getting any answer except "Tabs are bad,
> m'kay?".

Posit: White space is most often achieved by the user inserting a
sequence of space characters (U+0020).

Posit: Tab characters (U+0009) are, in a majority of environments,
rendered visually indistinguishable from a sequence of space
characters.

Corollary: most readers will, when seeing a stretch of white space on
a line, default to assuming that it represents a sequence of space
(U+0020) characters.

Corollary: So when a file containing either spaces or tabs is edited
in such an environment, the common way chosen by the user to get to
the same indentation level as existing lines is to prepend space
characters (using the spacebar or the Tab key or whatever facility the
editor provides) until the indentation lines up visually --
remembering the caveat that tabs and space-sequences are visually
indistinguishable in many environments.

Argument: The user will get an unexpected result when they do the
obvious thing (prepend space characters) in a tabs-only file. With
existing spaces-only files, the obvious way to get matching
indentation gives the expected result.

Conclusion: Thus, using tabs-only is inferior to using spaces-only for
indentation, because it violates the Principle of Least Astonishment
<URL:http://en.wikipedia.org/wiki/Principle_of_least_astonishment>.

-- 
 \             "I object to doing things that computers can do." —Olin |
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Ben Finney