Merge pull request RubyMoney#237 from cathper/master

Add exponent to currency

AUTHORS

@@ -7,6 +7,7 @@ banjerluke
 Bartosz Dz
 Bodaniel Jeanes
 bUg.
+Casper Thomsen
 Choongmin Lee
 Chris Kampmeier
 Christian Billen

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 - Ensure BigDecimal.new always receives a string - compatibility fix for ruby-1.9.2-p320
 - Update Maldivian Currency to MVR and fix ރ. to be ރ
+- Add exponent to currency
 
 ## 5.1.0
 

lib/money/currency.rb

@@ -139,6 +139,11 @@ def stringify_keys
     # @return [Integer]
     attr_reader :subunit_to_unit
 
+    # The number of digits after the decimal separator.
+    #
+    # @return [Float]
+    attr_reader :exponent
+
     # The decimal mark, or character used to separate the whole unit from the subunit.
     #
     # @return [String]
@@ -244,7 +249,7 @@ def hash
     # @example
     #   Money::Currency.new(:usd) #=> #<Currency id: usd ...>
     def inspect
-      "#<#{self.class.name} id: #{id}, priority: #{priority}, symbol_first: #{symbol_first}, thousands_separator: #{thousands_separator}, html_entity: #{html_entity}, decimal_mark: #{decimal_mark}, name: #{name}, symbol: #{symbol}, subunit_to_unit: #{subunit_to_unit}, iso_code: #{iso_code}, iso_numeric: #{iso_numeric}, subunit: #{subunit}>"
+      "#<#{self.class.name} id: #{id}, priority: #{priority}, symbol_first: #{symbol_first}, thousands_separator: #{thousands_separator}, html_entity: #{html_entity}, decimal_mark: #{decimal_mark}, name: #{name}, symbol: #{symbol}, subunit_to_unit: #{subunit_to_unit}, exponent: #{exponent}, iso_code: #{iso_code}, iso_numeric: #{iso_numeric}, subunit: #{subunit}>"
     end
 
     # Returns a string representation corresponding to the upcase +id+
@@ -281,6 +286,13 @@ def symbol_first?
       !!@symbol_first
     end
 
+    # Returns the number of digits after the decimal separator.
+    #
+    # @return [Float]
+    def exponent
+      Math.log10(@subunit_to_unit)
+    end
+
     # Cache decimal places for subunit_to_unit values.  Common ones pre-cached.
     def self.decimal_places_cache
       @decimal_places_cache ||= {

spec/currency_spec.rb

@@ -91,7 +91,7 @@
   describe "#inspect" do
     it "works as documented" do
       Money::Currency.new(:usd).inspect.should ==
-          %Q{#<Money::Currency id: usd, priority: 1, symbol_first: true, thousands_separator: ,, html_entity: $, decimal_mark: ., name: United States Dollar, symbol: $, subunit_to_unit: 100, iso_code: USD, iso_numeric: 840, subunit: Cent>}
+          %Q{#<Money::Currency id: usd, priority: 1, symbol_first: true, thousands_separator: ,, html_entity: $, decimal_mark: ., name: United States Dollar, symbol: $, subunit_to_unit: 100, exponent: 2.0, iso_code: USD, iso_numeric: 840, subunit: Cent>}
     end
   end
 
@@ -121,6 +121,14 @@
     end
   end
 
+  describe "#exponent" do
+    it "conforms to iso 4217" do
+      Money::Currency.new(:jpy).exponent == 0
+      Money::Currency.new(:usd).exponent == 2
+      Money::Currency.new(:iqd).exponent == 3
+    end
+  end
+
   describe "#decimal_places" do
     it "proper places for known currency" do
       Money::Currency.new(:mro).decimal_places == 1