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money.rb
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money.rb
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describe "Money" do
it "multiplies without side effects" do
first = Money.dollar(5)
first.times(2).should == Money.dollar(10)
first.times(3).should == Money.dollar(15)
second = Money.franc(5)
second.times(2).should == Money.franc(10)
second.times(3).should == Money.franc(15)
end
it "compares different currencies" do
Money.franc(5).should_not == Money.dollar(5)
end
it "rounds amounts correctly" do
end
it "keeps amount private" do
lambda { Money.dollar(0).amount = 1 }.should raise_error
end
it "implements equality comparison" do
Money.dollar(5).should == Money.dollar(5)
Money.dollar(6).should_not == Money.dollar(5)
Money.franc(5).should == Money.franc(5)
Money.franc(6).should_not == Money.franc(5)
Money.franc(6).should_not == Money.dollar(5)
end
it "implements a hash function" do
end
it "compares correctly to nil" do
end
it "compares correctly with another object" do
end
it "retrieves currencies correctly" do
Money.dollar(1).currency.should == "USD"
Money.franc(1).currency.should == "CHF"
end
it "does simple addition" do
five = Money.dollar(5)
sum = Expression.new(five.plus(five))
bank = Bank.new
reduced = bank.reduce(sum,"USD")
Money.dollar(10).should == reduced
six = Money.dollar(6)
sum = Expression.new(six.plus(five))
bank = Bank.new
reduced = bank.reduce(sum, "USD")
Money.dollar(11).should == reduced
end
it "reduces money correctly" do
five = Money.dollar(5)
bank = Bank.new
reduced = bank.reduce(five, "USD")
Money.dollar(5).should == reduced
end
it "reduces different currency correctly" do
bank = Bank.new
bank.add_rate("USD","CHF",2)
reduced = bank.reduce(Money.franc(2),"USD")
Money.dollar(1).should == reduced
end
end
#----------------------------------------
class Bank
def reduce(source, to)
source.reduce(self,to)
end
def add_rate(from,to,amount)
end
def rate(from,to)
( ("CHF" == from) && ("USD" == to)) ? 2 : 1
end
end
class Money
attr_reader :amount, :currency
def initialize(amount,currency)
@amount = amount
@currency = currency
end
def self.dollar(initial)
Money.new(initial,"USD")
end
def self.franc(initial)
Money.new(initial,"CHF")
end
def ==(other)
self.amount == other.amount and self.currency == other.currency
end
def times(multiplier)
Money.new((@amount * multiplier), @currency)
end
def plus(addend)
[ self, addend ]
# [ Money.new((amount+addend.amount), @currency) ]
end
def reduce(bank,to)
rate = bank.rate(@currency,to)
Money.new(@amount/rate, to)
# puts self.inspect
# self
end
def +(other)
@amount += other.amount
end
end
class Expression
attr_reader :list
def initialize(term)
@list = []
@list += term
# term.each { |x| Money.new(x.amount,x.currency)}
end
def reduce(bank,to)
total = 0
list.each { |money| total += money.amount }
Money.new(total,to)
end
end
class Pair
def initialize(first,second)
@first = first
@second = second
end
def ==(other)
( @first == other.first ) && ( @second == other.second )
end
end