From: Gary Wright <gwtmp01@...>
Date: 2012-01-28T06:24:35+09:00
Subject: Re: Microrant on Ruy's Math Skills


On Jan 27, 2012, at 3:52 PM, Chad Perrin wrote:
> Look back at the beginning of what I said.  It boils down to this:
> 
> One or two alternate comparison methods for Float that have known, clear,
> easily reasoned boundaries between where it works and where it does not,
> should be pretty easy to include in the Float implementation -- and to
> make succinct so we don't have to deal with fugliness in our code at
> every turn when dealing with decimal numbers.

Now we disagree. Trying to shoe-horn Floats into behaving like fixed point
numeric values is just the wrong approach. I understand wanting to have
a standard comparison method for Float but I don't think that is a
useful solution when you really want fixed point math (i.e. wrong tool
for the job but still a useful tool to have for other jobs).

Tony's suggestions seem like a better path to me:
> I think the real path forward here would be to propose that BigDecimal is
> loaded by default in Ruby 2.0, and to propose some type of literal
> representation for them, such as 1.1D that was suggested before.
> 
> The thing that stops people from using BigDecimal right now is the
> inconvenience of doing BigDecimal("1.1"), and the output of BigDecimal#to_s
> and #inspect is difficult to interpret.

I do think though that the syntax/convenience thing is somewhat of a distraction.

In any real program (i.e. not some one-off examples via irb), you aren't going
to be coding explicit constructors for BigDecimal or any other numeric type. It
will be something more like:

	sample.temperature = params['temperature']

Where you've previously defined the setter to do conversion from strings:

	def temperature=(text_value)
	  self['temperature'] = BigDecimal(text_value)
        end

In rails you can define a column to be of type :decimal and have the framework
manage all the conversion to/from BigDecimal.  I think this is the more typical
way that fixed-point math would be handled in a real program (i.e. via the
framework or library).


Gary Wright