Reconsiders responsibility of constructor in binary exercise (#499)

binary: Reconsiders responsibility of constructor

exercises/binary/.version

@@ -1 +1 @@
-2
+3

exercises/binary/binary_test.rb

@@ -5,83 +5,82 @@
 require_relative 'binary'
 
 # Test data version:
-# 01092b0
+# 82eb00d
 class BinaryTest < Minitest::Test
   def test_binary_0_is_decimal_0
     # skip
-    assert_equal 0, Binary.new('0').to_decimal
+    assert_equal 0, Binary.to_decimal('0')
   end
 
   def test_binary_1_is_decimal_1
     skip
-    assert_equal 1, Binary.new('1').to_decimal
+    assert_equal 1, Binary.to_decimal('1')
   end
 
   def test_binary_10_is_decimal_2
     skip
-    assert_equal 2, Binary.new('10').to_decimal
+    assert_equal 2, Binary.to_decimal('10')
   end
 
   def test_binary_11_is_decimal_3
     skip
-    assert_equal 3, Binary.new('11').to_decimal
+    assert_equal 3, Binary.to_decimal('11')
   end
 
   def test_binary_100_is_decimal_4
     skip
-    assert_equal 4, Binary.new('100').to_decimal
+    assert_equal 4, Binary.to_decimal('100')
   end
 
   def test_binary_1001_is_decimal_9
     skip
-    assert_equal 9, Binary.new('1001').to_decimal
+    assert_equal 9, Binary.to_decimal('1001')
   end
 
   def test_binary_11010_is_decimal_26
     skip
-    assert_equal 26, Binary.new('11010').to_decimal
+    assert_equal 26, Binary.to_decimal('11010')
   end
 
   def test_binary_10001101000_is_decimal_1128
     skip
-    assert_equal 1128, Binary.new('10001101000').to_decimal
+    assert_equal 1128, Binary.to_decimal('10001101000')
   end
 
   def test_binary_ignores_leading_zeros
     skip
-    assert_equal 31, Binary.new('000011111').to_decimal
+    assert_equal 31, Binary.to_decimal('000011111')
   end
 
   def test_2_is_not_a_valid_binary_digit
     skip
-    assert_raises(ArgumentError) { Binary.new('2') }
+    assert_raises(ArgumentError) { Binary.to_decimal('2') }
   end
 
   def test_a_number_containing_a_non_binary_digit_is_invalid
     skip
-    assert_raises(ArgumentError) { Binary.new('01201') }
+    assert_raises(ArgumentError) { Binary.to_decimal('01201') }
   end
 
   def test_a_number_with_trailing_non_binary_characters_is_invalid
     skip
-    assert_raises(ArgumentError) { Binary.new('10nope') }
+    assert_raises(ArgumentError) { Binary.to_decimal('10nope') }
   end
 
   def test_a_number_with_leading_non_binary_characters_is_invalid
     skip
-    assert_raises(ArgumentError) { Binary.new('nope10') }
+    assert_raises(ArgumentError) { Binary.to_decimal('nope10') }
   end
 
   def test_a_number_with_internal_non_binary_characters_is_invalid
     skip
-    assert_raises(ArgumentError) { Binary.new('10nope10') }
+    assert_raises(ArgumentError) { Binary.to_decimal('10nope10') }
   end
 
   def test_a_number_and_a_word_whitespace_spearated_is_invalid
     skip
-    assert_raises(ArgumentError) { Binary.new('001 nope') }
+    assert_raises(ArgumentError) { Binary.to_decimal('001 nope') }
   end
-
   # Problems in exercism evolve over time, as we find better ways to ask
   # questions.
   # The version number refers to the version of the problem you solved,
@@ -98,9 +97,8 @@ def test_a_number_and_a_word_whitespace_spearated_is_invalid
   #
   # If you are curious, read more about constants on RubyDoc:
   # http://ruby-doc.org/docs/ruby-doc-bundle/UsersGuide/rg/constants.html
-
   def test_bookkeeping
     skip
-    assert_equal 2, BookKeeping::VERSION
+    assert_equal 3, BookKeeping::VERSION
   end
 end

exercises/binary/example.rb

@@ -1,25 +1,25 @@
 module BookKeeping
-  VERSION = 2
+  VERSION = 3
 end
 
 class Binary
-  attr_reader :digits
+  def self.to_decimal binary
+    fail ArgumentError.new("invalid binary input #{binary}") if invalid?(binary)
 
-  def initialize(s)
-    fail ArgumentError.new("invalid binary input #{s}") unless valid?(s)
-
-    @digits = s.chars.reverse.collect(&:to_i)
+    digits(binary).reduce(0, &method(:convert))
   end
 
-  def to_decimal
-    digits.each_with_index.inject(0) do |decimal, (digit, i)|
-      decimal + digit * 2**i
-    end
+  private
+
+  def self.invalid?(binary)
+    binary =~ /[^01]/
   end
 
-  private
+  def self.digits(binary)
+    binary.chars.map(&:to_i)
+  end
 
-  def valid?(s)
-    s.chars.all? { |char| ['0', '1'].include?(char) }
+  def self.convert(decimal, digit)
+    decimal * 2 + digit
   end
 end

lib/binary_cases.rb

@@ -4,8 +4,7 @@ def name
   end
 
   def assertion
-    return error_assertion if raises_error?
-    equality_assertion
+    raises_error? ? error_assertion : equality_assertion
   end
 
   def skipped
@@ -23,7 +22,7 @@ def equality_assertion
   end
 
   def work_load
-    "Binary.new('#{binary}')#{'.to_decimal' unless raises_error?}"
+    "Binary.to_decimal('#{binary}')"
   end
 
   def raises_error?