Ruby 取消对象创建

Question

如果参数错误，如何取消对象创建？示例:

class MyClass
    def initialize(a, b, c)
        @a = @b = @c = nil
        @a = a if a.is_a? Integer
        @b = b if b.is_a? String
        @c = c if c.is_a? Integer or c.is_a? Float
        return nil if @a == nil or @b == nil or @c == nil # doesn't works
    end
end
cl = MyClass.new('str', 'some', 1.0) # need cl to be nil because 1st param isn't Integer

Answer 1

很简单，不用构造器就行了。 :)

class MyClass
  def initialize(a, b, c)
    @a, @b, @c = a, b, c
  end

  def self.fabricate(a, b, c)
    aa = a if a.is_a? Integer
    bb = b if b.is_a? String
    cc = c if c.is_a? Integer || c.is_a? Float
    return nil unless aa && bb && cc
    new(aa, bb, cc)
  end
end

cl = MyClass.fabricate('str', 'some', 1.0) # => nil

顺便说一句，这个模式叫做工厂方法。