Ruby oddities (or "what's 1.0 divided by 0.0?")

Published: Apr 9, 2007

Working very closely with the source code of MRI (Matz's Ruby Implementation, a term used to distinguish the main Ruby implementation from the language itself) has exposed me to some of Ruby's most... interesting behaviour. This is one:

irb(main):001:0> 1.0 / 0.0
=> Infinity
irb(main):002:0> 1.0.divmod(0.0)[0]
=> NaN
irb(main):003:0> 1.0.div(0.0)
FloatDomainError: Infinity
        from (irb):3:in `div'
        from (irb):3

And no, Infinity does not equal NaN, and they're not related in terms of inheritance or anything like that; they're completely different values. Apparently, / follows the IEEE-754 standard (including in cases involving a negative zero), divmod probably follows intuitive mathematics (which I'm quite sure is not really correct because "1 / 0" has no meaning in strict mathematics), while @div@ follows a practice quite common in programming languages of raising an exception (though an odd one at that). Coupled with the fact that 1 / 0 raises a different exception (ZeroDivisionError), well... go figure.

vim tip: Modelines

In Vim, you can set per-file options using modelines. (This has nothing to do with the term "mode line" in Emacs. Emacs has a similar feature, but I don't know what it's called there.) Basically they are special strings in the first or last few lines of a file that Vim interprets into options. They look like, for example, // vim: expandtab. The exact syntax is explained in detail in the [modeline](http://vimdoc.sourceforge.net/htmldoc/options.html#modeline) section of Vim's help.

Restored from VimTips archive

This article was restored from the VimTips archive. There's probably missing images and broken links (and even some flash references), but it was still important to me to bring them back.

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Programming