在Ruby中输入转换：“正确”的方式？

I am trying to decide if a string is a number in Ruby. This is my code

我想确定一个字符串是否是Ruby中的数字。这是我的代码

whatAmI = "32.3a22"
puts "This is always false " + String(whatAmI.is_a?(Fixnum));
isNum = false;
begin
  Float(whatAmI)
  isNum = true;
rescue Exception => e
  puts "What does Ruby say? " + e
  isNum = false;
end
puts isNum

I realize that I can do it with a RegEx, but is there any standard way to do it that I'm missing? I've seen a can_convert? method, but I don't seem to have it.

我意识到我可以使用RegEx做到这一点,但有没有任何标准的方法可以做到这一点我错过了?我见过can_convert?方法,但我似乎没有。

Is there a way to add a can_convert? method to all Strings? I understand that it's possible in Ruby. I also understand that this may be totally unecessary...

有没有办法添加can_convert?所有字符串的方法?我知道在Ruby中它是可能的。我也明白这可能是完全不必要的......

Edit The to_f methods do not work, as they never throw an Exception but rather just return 0 if it doesn't work out.

编辑to_f方法不起作用,因为它们从不抛出异常,而只是返回0,如果它没有用完。

3 个解决方案

#1

You've got the right idea. It can be done a little more compactly, though:

你有正确的想法。但它可以做得更紧凑一点:

isNum = Float(whatAmI) rescue nil

Inlining "rescue" is great fun. Parenthesize the part you're rescuing if you put it in the middle of more stuff, like:

内联“救援”非常有趣。如果你把它放在更多东西的中间,请将你正在营救的部分括号括起来,例如:

if (isNum = Float(whatAmI) rescue nil) && isNum > 20
  ...

#2

This might sound overly critical, but based on your description, you're almost certainly doing something "wrong"... Why would you need to check whether a String is a valid representation of a Float but not actually convert the String?

这可能听起来过于关键,但根据您的描述,您几乎肯定会做一些“错误的”...为什么您需要检查String是否是Float的有效表示但实际上不转换String?

This is just a hunch, but it may be useful to describe what you're trying to accomplish. There's probably a "better" way.

这只是一种预感,但描述您想要实现的目标可能很有用。可能有一种“更好”的方式。

For example, you might want to insert the String into a database and put together an sql statement using string concatenation. It would be preferable to convert to a Float and use prepared statements.

例如,您可能希望将String插入数据库并使用字符串连接将sql语句放在一起。最好转换为Float并使用预处理语句。

If you just need to inspect the "shape" of the string, it would be preferable to use a regular expression, because, as dylan pointed out, a Float can be represented in any number of ways that may or may not be appropriate.

如果你只需要检查字符串的“形状”,最好使用正则表达式,因为正如dylan所指出的,Float可以用任何可能适合或不适合的方式表示。

You may also have to deal with international input, in Europe, a comma is used instead of a period as decimal seperator, yet Ruby Floats have to use the (.).

您可能还需要处理国际输入,在欧洲,使用逗号而不是作为十进制分隔符的句点,但Ruby Floats必须使用(。)。

#3

I don't know about the can_convert method, but generally a class will define methods like to_s, to_i, to_hash and so on. These methods return a different representation of the object, for example, a to_s method will return a string representation of an object.

我不知道can_convert方法,但通常一个类将定义像to_s,to_i,to_hash等方法。这些方法返回对象的不同表示形式,例如,to_s方法将返回对象的字符串表示形式。

As for the actual converting, I'm sure someone else can answer that better than me.

至于实际的转换,我相信其他人可以比我更好地回答。

On another note, if you're wondering if you can add a method to all strings, you can. Just open up the String class and add it!

另外请注意,如果您想知道是否可以为所有字符串添加方法,则可以。只需打开String类并添加它!

class String
  def can_convert?
    ...
  end
end

Edit: Strings containing exponential notation are supported by to_f.

编辑:to_f支持包含指数表示法的字符串。

>> "6.02e23".to_f
=> 6.02e+23

#1