Test if a string is basically an integer in quotes using Ruby?

Question

I need a function, is_an_integer, where

"12".is_an_integer? returns true
"blah".is_an_integer? returns false

how can i do this in ruby? i would write a regex but im assuming there is a helper for this that i am not aware of

Answer 1

You can use Integer(str) and see if it raises:

def is_num?(str)
  Integer(str)
rescue ArgumentError
  false
else
  true
end

Addendum: It should be pointed out that while this does return true for "01", it does not for "09", simply because 09 would not be a valid integer literal.

Answer 2

Well, here's the easy way:

class String
  def is_integer?
    self.to_i.to_s == self
  end
end

>> "12".is_integer?
=> true
>> "blah".is_integer?
=> false

EDIT: I don't agree with the solutions that provoke an exception to convert the string - exceptions are not control flow, and you might as well do it the right way. That said, my solution above doesn't deal with non-base-10 integers. So here's the way to do with without resorting to exceptions:

  class String
    def integer? 
      [                          # In descending order of likeliness:
        /^[-+]?[1-9]([0-9]*)?$/, # decimal
        /^0[0-7]+$/,             # octal
        /^0x[0-9A-Fa-f]+$/,      # hexadecimal
        /^0b[01]+$/              # binary
      ].each do |match_pattern|
        return true if self =~ match_pattern
      end
      return false
    end
  end

Answer 3

class String
  def integer?
    Integer(self)
    return true
  rescue ArgumentError
    return false
  end
end

1. It isn't prefixed with is_. I find that silly on questionmark methods, I like "04".integer? a lot better than "foo".is_integer?.
2. It uses the sensible solution by sepp2k, which passes for "01" and such.
3. Object oriented, yay.

Answer 4

You can use regular expressions:

def isint(str)
   return str =~ /^[-+]?[0-9]+$/
end

heh ... first time coding in ruby ... huray!

[edit] here is the function with janm's suggestions .. thanks man!

class String
    def is_i?
       !!(self =~ /^[-+]?[0-9]+$/)
    end
end

[/edit]

Answer 5

You can do a one liner:

str = ...
int = Integer(str) rescue nil

if int
  int.times {|i| p i}
end

or even

int = Integer(str) rescue false

Depending on what you are trying to do you can also directly use a begin end block with rescue clause:

begin
  str = ...
  i = Integer(str)

  i.times do |j|
    puts j
  end
rescue ArgumentError
  puts "Not an int, doing something else"
end