Add converting numbers text, specs, and solution

Author: paulgoetze

2_Numbers/2_Basic_operators/solution.rb

@@ -1,4 +1,4 @@
-# e.g.
+# e.g.:
 sum = Rational(1, 3) + Rational(2)
 difference = 1_000_000_000_000_000_000_000_000 - 1.9
 product = 2.4 * 5.6 * 2.3

2_Numbers/3_Converting_numbers/solution.rb

@@ -0,0 +1,5 @@
+# e.g.:
+integer = Complex(2.5).to_i
+float = 42.to_f
+rational = 10.25.to_r
+complex = Rational(1.1, 3.3).to_c

2_Numbers/3_Converting_numbers/solution_spec.rb

@@ -0,0 +1,75 @@
+require 'rspec'
+require 'rspec/expectations'
+
+# requires code_breaker gem to be installed
+# (https://github.com/daigaku-ruby/code_breaker)
+require 'code_breaker'
+
+RSpec::Matchers.define :run_number_conversions do |expected|
+  METHODS = {
+    to_i: 'to integer',
+    to_f: 'to float',
+    to_r: 'to Rational number',
+    to_c: 'to Complex number'
+  }
+
+  match do |actual|
+    lines = actual.split("\n").compact.map(&:strip).reject(&:empty?)
+    called_conversions(lines).include?(expected)
+  end
+
+  def called_conversions(lines)
+    lines.map { |line|
+      CodeBreaker.parse(line) unless line.start_with?('#')
+    }.compact
+  end
+
+  failure_message do |actual|
+    expected_operants = expected.values.first
+    variable_name = expected_operants[0]
+
+    expected_method = METHODS[expected_operants[1][1]]
+    expected_conversion = "#{variable_name} = #{expected_operants[1][0]} #{expected_method}"
+
+    actual_line = actual.split("\n").select do |output|
+      output.match(/#{variable_name} =.+/)
+    end
+
+    actual_parsed = CodeBreaker.parse(actual_line.join)
+    actual_operants = actual_parsed.values.first
+    actual_conversion = "#{variable_name} = #{[actual_operants[1]].flatten.join(' ')}"
+
+    %Q{Your code doesn't run the number conversion "#{expected_conversion}".
+      ------- Instead you defined "#{actual_conversion}".}
+  end
+end
+
+# code_breaker outputs
+CONVERSIONS = [
+  { lvasgn: [:integer, [Complex, :to_i]] },
+  { lvasgn: [:float, [Fixnum, :to_f]] },
+  { lvasgn: [:rational, [Float, :to_r]] },
+  { lvasgn: [:complex, [Rational, :to_c]] }
+].freeze
+
+describe "Your code" do
+  [['solution::code']]
+
+  CONVERSIONS.each do |conversion|
+    variable_name = conversion.first.last.first
+    values = conversion.values.first.last
+
+    it "defines a variable with name \"#{variable_name}\"" do
+      expect(local_variables.include?(variable_name)).to be true
+    end
+
+    if local_variables.include?(variable_name)
+      article = !!variable_name.match(/^[eioa]/) ? 'an' : 'a'
+
+      it "converts a #{values.first} number to #{article} #{variable_name}" do
+        code_lines = %Q{ [['solution::code']] }
+        expect(code_lines).to run_number_conversions(conversion)
+      end
+    end
+  end
+end

2_Numbers/3_Converting_numbers/task.md

@@ -7,10 +7,50 @@
 
 ---
 
-There are several methods you can apply on numbers to convert a number to another
-number format:
+There are several methods you can apply on numbers to explicitly convert a number
+to another number format:
 
-`to_i` converts to an Integer number
-`to_f` converts to a Float number
-`to_r` converts to a Rational values
-`to_c` converts to a Complex number
+`  to_i` converts to an *Integer* number
+`  to_f` converts to a *Float* number
+`  to_r` converts to a *Rational* values
+`  to_c` converts to a *Complex* number
+
+Converting a number to its own type will just return the number, e.g.:
+
+`  123.to_i`                *# => 123*
+`  4.75.to_f`               *# => 4.75*
+`  Rational(3, 7).to_r`     *# => (3,7)*
+`  Complex(2.1, 3.2).to_c`  *# => (2.1+3.2i)*
+
+If you convert a Float, a Rational or a Complex number to an Integer by calling
+the `to_i` method then the digits after the decimal point are just cut off.
+Note that the size of the fraction doesn't matter:
+
+`  2.01.to_i` and `2.95.to_i` will both return *2*.
+
+If you want to convert a float to an integer based on its digits after the decimal point,
+you should have a look at the `#floor`, `#ceil`, and `#round` methods of a Numeric:
+
+-  (ruby-doc core: Numeric#ceil)
+-  (ruby-doc core: Numeric#floor)
+-  (ruby-doc core: Numeric#round)
+
+One thing you can't do is converting a Complex number with an imaginary part other
+than `0` to an integer, float, or rational number.
+
+For instance `Complex(5.3, 0.5).to_i` will throw an Error (*RangeError: can't convert 5.3+0.5i into Integer*),
+whereas `Complex(5.3).to_i` will give you a *5*.
+
+---
+
+Convert numbers into other formats:
+
+1. Convert a *Complex* number into an *Integer*
+2. Convert a *Fixnum* integer into a *Float*
+3. Convert a *Float* into a *Rational* number
+4. Convert a *Rational* number into an *Complex* number
+
+Store each result in a variable that is named like the resulting type of the conversion, e.g.
+for 1. *integer*,
+for 2. *float*,
+and so on.