From: Florian Gilcher <flo@...>
Date: 2012-01-30T18:01:02+09:00
Subject: Re: Microrant on Ruy's Math Skills


On Jan 30, 2012, at 9:32 AM, Tony Arcieri wrote:

> On Mon, Jan 30, 2012 at 12:22 AM, Robert Klemme
> <shortcutter@googlemail.com>wrote:
> 
>> It seems many people use the "floating point mess" without major
>> issues.  So it cannot be as bad as you make it sound.
>> 
> 
> Floating points are a great choice for approximating continuous values and
> thus working on things which require both high performance and
> approximating real-world data sources. This includes things like games,
> non-gaming related 3D applications, perceptual media including audio and
> video codecs, and everything involved in working with perceptual media on
> computers such as non-linear editing, speech synthesis, and speech
> recognition.

Let me add "statistics gathering" to the list...

> People don't often do these things in Ruby. I'd say they're uncommon use
> cases.

... and suddenly, you have a _very_ common use case. I have no client
where it doesn't happen.

Graphing is also not uncommon.

> 
> Something people do quite often in Ruby: deal with money. Money isn't
> continuous, it's discrete. A decimal type is a much better choice for
> dealing with money than a floating point.

Yes, but a dedicated money type that encodes the currency is also a much better
choice. Also the standard in handling monetary values is not using a decimal
representation anyways: you just encode the smallest value as an Integer.

> As I said before, I think Ruby could benefit from decimal literals. They
> can't solve all use cases. They can't be a replacement for rationals, such
> as in the 1D/3D example (actually I'm not entirely convinced of that
> either, but that's a sidebar)
> I have found many uses for BigDecimal before and have seen Fixnums used
> where BigDecimal would probably be more appropriate (i.e. "count cents, not
> dollars!") where having (Big)Decimal literals would probably change
> people's minds about that sort of thing.

Counting cents is perfectly valid, fits every database (even your fancy NOSQL
database that doesn't have a decimal type) and is the proper way to do math 
involving money. The base value is not the Dollar, it is the
cent. This doesn't hold true if you venture into the realms of fractional
cents, but thats really uncommon (an can be solved by using Rational).

If money is the reason against float, its the wrong reason. It may be a tempting
error, but it only shows that the developer in question did not read a single 
line about handling money in software - which is another common problem, but
not one that you can actually fix by the choice of literals.