Ruby 的 Number 类和 0 的便捷方法 [英] Convenience methods for Ruby's Number class and 0

问题描述

我正在编写方便的方法来检查数字是正数还是负数，如下所示:

I'm writing convenience methods to check if number is positive or negative like so:

class Numeric
  def positive?
    self > 0
  end

  def negative?
    self < 0
  end
end

但在这种情况下我不知道如何处理这样的情况:

but in this case I do not know how to handle cases like these:

>> 0.positive?
>> 0.negative?

更新:我更新了班级名称中的拼写错误.我使用数字是因为我还需要检查浮点数.

Update: I've updated the typo in the class name. I used numeric because I needed to check the floats as well.

推荐答案

如果问题是两者都得到 false，那么您可以将 0 视为积极与否.如果是这样，你应该有类似的东西:

If the problem is that you're getting false for both, either you consider 0 to be positive or not. If so, you should have something like:

def positive?
    self >= 0
end

如果不是，就保持原样，因为 0 既不是正也不是负，你应该对两者都返回 false.

If not, leave it as it is, since 0 is neither positive not negative and you should return false for both.

但是，如果问题是 0.positive? 出现错误(更有可能)，则出现问题的原因是 0是 FixNum，而不是 Number.您可以通过以下消息看到这一点:

However if the problem is that you're getting errors with 0.positive? (far more likely), the reason you're getting a problem is because 0 is a FixNum, not a Number. You can see that with the following message:

testprog.rb:12: undefined method `positive?' for 0:Fixnum (NoMethodError)

您可能应该将它添加到 Fixnum 本身，或 Integer，或 Numeric，各种数字类型的基类，如 FixNum 和 BigNum.您在何处注入便利方法取决于您希望它们在多大范围内可用.

You should probably add it to Fixnum itself, or Integer, or Numeric, the base class for various numeric types like FixNum and BigNum. Where you inject your convenience methods depends on how widely you want them available.

例如，如果您将代码更改为以下内容(我在此处包含测试代码):

For example, if you change your code to the following (I'm including test code here):

class Numeric
    def positive?
        self > 0
    end

    def negative?
        self < 0
    end
end

print " 0 positive?: ",  0.positive?,"\n"
print " 0 negative?: ",  0.negative?,"\n"
print " 0 zero?    : ",  0.zero?,"\n\n"

print "99 positive?: ", 99.positive?,"\n"
print "99 negative?: ", 99.negative?,"\n"
print "99 zero?    : ", 99.zero?,"\n\n"

print "-2 positive?: ", -2.positive?,"\n"
print "-2 negative?: ", -2.negative?,"\n"
print "-2 zero?    : ", -2.zero?,"\n\n"

然后它工作正常，输出:

it then works fine, outputting:

 0 positive?: false
 0 negative?: false
 0 zero?    : true

99 positive?: true
99 negative?: false
99 zero?    : false

-2 positive?: false
-2 negative?: true
-2 zero?    : false

正如预期的那样.

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