Pretty Floats

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Today, I would like to get pretty printing of Float instances working. Specifically I would like:

• 1.125.to_s == '1⅛'
• 1.25.to_s == '1¼'
• 0.875.to_s == '⅞'

First up, I describe existing behavior that should not change:

describe Float, "pretty printing" do
  specify "1.23.to_s == '1.23'" do
    1.23.to_s.should == "1.23"
  end

As expected, that example passes without any changes. Next up, I describe precision. There is no reason to specify more than two decimal points when trying to measure things, so, in RSpec format:

  specify "1.236.to_s == '1.24'" do
    1.236.to_s.should == "1.24"
  end

That fails with:

1)
'Float to_s should only include 2 decimals precision' FAILED
expected: "1.24",
     got: "1.236" (using ==)
./spec/float_spec.rb:8:

To get that to pass, I re-open the Float to override to_s:

class Float
  def to_s
    "%.2f" % self
  end
end

The updated Float class is not automatically included in my Sinatra application (and thus in the RSpec examples). I save it in the lib directory, and then add this to the Sinatra application:

$: << File.expand_path(File.dirname(__FILE__) + '/lib')

require 'float'

For the remaining numbers that are likely to appear in recipes using imperial units of measure, I use these examples:

  specify "0.25.to_s == '¼'"
  specify "0.5.to_s == '½'"
  specify "0.75.to_s == '¾'"
  specify "0.33.to_s == '⅓'"
  specify "0.66.to_s == '⅔'"
  specify "0.125.to_s == '⅛'"
  specify "0.325.to_s == '⅜'"
  specify "0.625.to_s == '⅝'"
  specify "0.875.to_s == '⅞'"

I end up using a long case statement to get that passing:

class Float
  def to_s
    int = self.to_i
    frac = pretty_fraction(self - int)

    if frac
      (int == 0 ? "" : int.to_s) + frac
    else
      "%.2f" % self
    end
  end

  private

  def pretty_fraction(fraction)
    case fraction
    when 0.25
      "¼"
    when 0.5
      "½"
    when 0.75
      "¾"
    when 0.33
      "⅓"
    when 0.66
      "⅔"
    when 0.125
      "⅛"
    when 0.325
      "⅜"
    when 0.625
      "⅝"
    when 0.875
      "⅞"
    end
  end
end

In addition to pretty printing things that look like fractions, I also want to print things that look like integers:

  specify "1.0.to_s == '1'" do
    1.0.to_s.should == "1"
  end

I get that to pass with another condition on the case statement:

    case fraction
...
    when 0
      ""
    end

Last up is a need to account for the cases when the author goes overboard with precision. That is, what happens if I entered 0.67 or 0.667 to mean two-thirds. In RSpec:

  specify "0.33.to_s == '⅓'" do
    0.33.to_s.should == "⅓"
  end
  specify "0.333.to_s == '⅓'" do
    0.333.to_s.should == "⅓"
  end
  specify "0.66.to_s == '⅔'" do
    0.66.to_s.should == "⅔"
  end
  specify "0.667.to_s == '⅔'" do
    0.667.to_s.should == "⅔"
  end

Rather than account for all possible cases, I use a range in my case statement:

  def pretty_fraction(fraction)
    case fraction
...
    when 0.33..0.34
      "⅓"
    when 0.66..0.67
      "⅔"
...
    end
  end

This makes use of case statements performing a triple equality operation on the target and that:

>> (0.66..0.67) === 0.666
=> true

With my floats printing nicely, I have cleared up the most bothersome of the minor issues that I found on the beta site. Tomorrow, I will work through a few more issues and redeploy.