[ruby/bigdecimal] Add Complex#to_d

https://github.com/ruby/bigdecimal/commit/97e794ac97

ext/bigdecimal/lib/bigdecimal/util.rb

@@ -131,6 +131,39 @@ class Rational < Numeric
 end
 
 
+class Complex < Numeric
+  # call-seq:
+  #     cmp.to_d             -> bigdecimal
+  #     cmp.to_d(precision)  -> bigdecimal
+  #
+  # Returns the value as a BigDecimal.
+  #
+  # The +precision+ parameter is required for a rational complex number.
+  # This parameter is used to determine the number of significant digits
+  # for the result.
+  #
+  #     require 'bigdecimal'
+  #     require 'bigdecimal/util'
+  #
+  #     Complex(0.1234567, 0).to_d(4)   # => 0.1235e0
+  #     Complex(Rational(22, 7), 0).to_d(3)   # => 0.314e1
+  #
+  # See also BigDecimal::new.
+  #
+  def to_d(*args)
+    BigDecimal(self) unless self.imag.zero? # to raise eerror
+
+    if args.length == 0
+      case self.real
+      when Rational
+        BigDecimal(self.real) # to raise error
+      end
+    end
+    self.real.to_d(*args)
+  end
+end
+
+
 class NilClass
   # call-seq:
   #     nil.to_d -> bigdecimal

test/bigdecimal/test_bigdecimal_util.rb

@@ -60,6 +60,18 @@ class TestBigDecimalUtil < Test::Unit::TestCase
     assert_raise(ArgumentError) { 355.quo(113).to_d(-42) }
   end
 
+  def test_Complex_to_d
+    assert_equal(BigDecimal("1"), Complex(1, 0).to_d)
+    assert_equal(BigDecimal("0.333333333333333333333"),
+                 Complex(1.quo(3), 0).to_d(21))
+    assert_equal(BigDecimal("0.1234567"), Complex(0.1234567, 0).to_d)
+    assert_equal(BigDecimal("0.1235"), Complex(0.1234567, 0).to_d(4))
+
+    assert_raise_with_message(ArgumentError, "can't omit precision for a Rational.") { Complex(1.quo(3), 0).to_d }
+
+    assert_raise_with_message(ArgumentError, "Unable to make a BigDecimal from non-zero imaginary number") { Complex(1, 1).to_d }
+  end
+
   def test_String_to_d
     assert_equal(BigDecimal('1'), "1__1_1".to_d)
     assert_equal(BigDecimal('2.5'), "2.5".to_d)