早上看了
Ruby论坛中有人（blackanger）写的TDD by Ex这本书里的资金例子，自己也想写一写。和他不同，我是全过程详细写出来。第一次用Ruby写代码，第一次用Ruby的Unit框架，而且下午睡醒后迷迷糊糊写的，可能有很多错误，请多多指正。
第一次迭代后的代码（简单的TDD代码）
# file tc_doller.rb
$:.unshift File.join(File.dirname(__FILE__), "..", "src")
require 'test/unit'
require 'dollar'
class TestMoney < Test::Unit::TestCase
def testMultiplication
five = Dollar.new(5)
five.times(2)
assert_equal(10, five.amount)
end
end
# file doller.rb
class Dollar
def initialize(amount)
@amount = amount
end
def times(multiplier)
@amount = @amount * multiplier
end
def amount
return @amount
end
end
第二次迭代后的代码
# file tc_doller.rb
$:.unshift File.join(File.dirname(__FILE__), "..", "src")
require 'test/unit'
require 'dollar'
class TestMoney < Test::Unit::TestCase
def testMultiplication
five = Dollar.new(5)
product = five.times(2)
assert_equal(10, product.amount)
product = five.times(3)
assert_equal(15, product.amount)
end
end
# file doller.rb
class Dollar
attr_reader :amount
protected :amount
def initialize(amount)
@amount = amount
end
def times(multiplier)
return Dollar.new @amount * multiplier
end
end
第三，四次迭代后的代码（添加了相等性测试，刚好Ruby中的equal?和==的语意和Java相反）
# file tc_doller.rb
$:.unshift File.join(File.dirname(__FILE__), "..", "src")
require 'test/unit'
require 'dollar'
class TestMoney < Test::Unit::TestCase
def testMultiplication
five = Dollar.new(5)
product = five.times(2)
assert_equal(10, product.amount)
product = five.times(3)
assert_equal(15, product.amount)
end
def testEquality
assert(Dollar.new(5) == Dollar.new(5))
assert(Dollar.new(5) != Dollar.new(6))
end
end
# file doller.rb
class Dollar
attr_reader :amount
protected :amount
def initialize(amount)
@amount = amount
end
def times(multiplier)
return Dollar.new @amount * multiplier
end
def ==(obj)
return obj.amount == @amount
end
end
第五，六，七次迭代后的代码（短命的Franc对象登场）
# file tc_doller.rb
$:.unshift File.join(File.dirname(__FILE__), "..", "src")
require 'test/unit'
require 'money'
require 'dollar'
require 'franc'
class TestMoney < Test::Unit::TestCase
def testMultiplication
five = Dollar.new(5)
assert_equal(Dollar.new(10), five.times(2))
assert_equal(Dollar.new(15), five.times(3))
end
def testEquality
assert(Dollar.new(5) == Dollar.new(5))
assert(Dollar.new(5) != Dollar.new(6))
assert(Franc.new(5) == Franc.new(5))
assert(Franc.new(5) != Franc.new(6))
assert(Franc.new(5) != Dollar.new(5))
end
def testFrancMultiplication
five = Franc.new(5)
assert_equal(Franc.new(10), five.times(2))
assert_equal(Franc.new(15), five.times(3))
end
end
# file doller.rb
class Dollar < Money
def initialize(amount)
super(amount)
end
def times(multiplier)
return Dollar.new(@amount * multiplier)
end
end
# file franc.rb
class Franc < Money
def initialize(amount)
super(amount)
end
def times(multiplier)
return Franc.new(@amount * multiplier)
end
end
# file money.rb
class Money
attr_reader :amount
protected :amount
def initialize(amount)
@amount = amount
end
def ==(obj)
return obj.amount.equal?(@amount)
end
end
第八，九，十，十一次迭代（消除子类，很巧妙的一步）
# file tc_doller.rb
$:.unshift File.join(File.dirname(__FILE__), "..", "src")
require 'test/unit'
require 'money'
class TestMoney < Test::Unit::TestCase
def testMultiplication
five = Money.dollar(5)
assert_equal(Money.dollar(10), five.times(2))
assert_equal(Money.dollar(15), five.times(3))
end
def testFrancMultiplication
five = Money.franc(5)
assert_equal(Money.franc(10), five.times(2))
assert_equal(Money.franc(15), five.times(3))
end
def testEquality
assert(Money.dollar(5) == Money.dollar(5))
assert(Money.dollar(5) != Money.dollar(6))
assert(Money.franc(5) != Money.dollar(5))
end
def testCurrency
assert_equal("USD", Money.dollar(1).currency)
assert_equal("CHF", Money.franc(1).currency)
end
end
# file money.rb
class Money
attr_reader :amount, :currency
protected :amount
def initialize(amount, currency)
@amount = amount
@currency = currency
end
def self.dollar(amount)
return Money.new(amount, "USD")
end
def self.franc(amount)
return Money.new(amount, "CHF")
end
def times(multiplier)
return Money.new(@amount*multiplier, @currency)
end
def plus(addend)
return Money.new(@amount + addend.amount, currency)
end
def ==(obj)
return obj.amount.equal?(@amount) && (obj.currency == @currency)
end
end
最后的一部分
最后是完成不同货币之间的计算，引入了两个新的对象负责处理汇率的Bank和货币相加的Sum对象。
由于Ruby的动态性无须让Sum和Money实现同一接口，反正原书中的Expression对象也是为了Sum和Money对象可以通信。或许可以把Sum简化掉，有空时再想想。
# file tc_doller.rb
$:.unshift File.join(File.dirname(__FILE__), "..", "src")
require 'test/unit'
require 'money'
require 'bank'
require 'sum'
class TestMoney < Test::Unit::TestCase
def testDollarMultiplication
five = Money.dollar(5)
assert_equal(Money.dollar(10), five.times(2))
assert_equal(Money.dollar(15), five.times(3))
end
def testFrancMultiplication
five = Money.franc(5)
assert_equal(Money.franc(10), five.times(2))
assert_equal(Money.franc(15), five.times(3))
end
def testEquality
assert(Object.new != Money.dollar(1))
assert(Money.dollar(5) == Money.dollar(5))
assert(Money.dollar(5) != Money.dollar(6))
assert(Money.franc(5) != Money.dollar(5))
end
def testCurrency
assert_equal("USD", Money.dollar(1).currency)
assert_equal("CHF", Money.franc(1).currency)
end
def testSimpleAddition
five = Money.dollar(5)
sum = five.plus(Money.dollar(5))
bank = Bank.new()
reduced = bank.reduce(sum, "USD")
assert_equal(Money.dollar(10), reduced)
end
def testReduceSum
sum = Sum.new(Money.dollar(3), Money.dollar(4))
bank = Bank.new()
result = bank.reduce(sum, "USD")
assert_equal(Money.dollar(7), result)
end
def testReduceMoney
bank = Bank.new
result = bank.reduce(Money.dollar(1), "USD")
assert_equal(Money.dollar(1), result)
end
def testReduceMoneyDiffentCurrency
bank = Bank.new
bank.addRate("CHF", "USD", 2)
result = bank.reduce(Money.franc(2), "USD")
assert_equal(Money.dollar(1), result)
end
def testIndentityRate
bank = Bank.new
bank.addRate("USD", "CHF", 0.5)
assert_equal(1, bank.rate("USD", "USD"))
assert_equal(0.5, bank.rate("USD", "CHF"))
assert_equal(2, bank.rate("CHF", "USD"))
end
def testMixedAddition
fiveBucks = Money.dollar(5)
tenFrancs = Money.franc(10)
bank = Bank.new
bank.addRate("CHF", "USD", 2)
result = bank.reduce(fiveBucks.plus(tenFrancs), "USD")
assert_equal(Money.dollar(10), result)
end
def testSumTimes
fiveBucks = Money.dollar(5)
tenFrancs = Money.franc(10)
bank = Bank.new
bank.addRate("CHF", "USD", 2)
sum = Sum.new(fiveBucks, tenFrancs).times(2)
result = bank.reduce(sum, "USD")
assert_equal(Money.dollar(20), result)
end
end
# file money.rb
class Money
attr_reader :amount, :currency
def initialize(amount, currency)
@amount = amount
@currency = currency
end
def self.dollar(amount)
return Money.new(amount, "USD")
end
def self.franc(amount)
return Money.new(amount, "CHF")
end
def times(multiplier)
return Money.new(@amount*multiplier, @currency)
end
def plus(addend)
return Sum.new(self, addend)
end
def ==(obj)
return obj.amount.equal?(@amount) && (obj.currency == @currency)
end
def reduce(bank, to)
rate = bank.rate(@currency, to)
return Money.new(@amount / rate, to)
end
end
# file bank.rb
class Bank
attr_accessor :rates
@@rates = {}
def reduce(source, to)
return source.reduce(self, to)
end
def addRate(from, to, rate)
@@rates["#{from}-#{to}"] = rate
@@rates["#{to}-#{from}"] = 1 / rate
end
def rate(from, to)
return 1 if(from == to)
return @@rates["#{from}-#{to}"]
end
end
# file sum.rb
class Sum
attr_reader :augend, :addend
def initialize(augend, addend)
@augend = augend
@addend = addend
end
def reduce(bank, to)
amount = augend.reduce(bank, to).amount + addend.reduce(bank, to).amount
return Money.new(amount, to)
end
def times(multiplier)
return Sum.new(augend.times(multiplier), addend.times(multiplier))
end
end