Checking if a variable is an integer

Question

Does Rails 3 or Ruby have a built-in way to check if a variable is an integer?

For example,

1.is_an_int #=> true
\"dadadad@asdasd.net\".is_an_int          


        

Answer 1

If you're uncertain of the type of the variable (it could be a string of number characters), say it was a credit card number passed into the params, so it would originally be a string but you want to make sure it doesn't have any letter characters in it, I would use this method:

    def is_number?(obj)
        obj.to_s == obj.to_i.to_s
    end

    is_number? "123fh" # false
    is_number? "12345" # true

@Benny points out an oversight of this method, keep this in mind:

is_number? "01" # false. oops!

Answer 2

In case you don't need to convert zero values, I find the methods to_i and to_f to be extremely useful since they will convert the string to either a zero value (if not convertible or zero) or the actual Integer or Float value.

"0014.56".to_i # => 14
"0014.56".to_f # => 14.56
"0.0".to_f # => 0.0
"not_an_int".to_f # 0
"not_a_float".to_f # 0.0

"0014.56".to_f ? "I'm a float" : "I'm not a float or the 0.0 float" 
# => I'm a float
"not a float" ? "I'm a float" : "I'm not a float or the 0.0 float" 
# => "I'm not a float or the 0.0 float"

EDIT2 : be careful, the 0 integer value is not falsey it's truthy (!!0 #=> true) (thanks @prettycoder)

EDIT

Ah just found out about the dark cases... seems to only happen if the number is in first position though

"12blah".to_i => 12

Answer 3

You can use triple equal.

if Integer === 21 
    puts "21 is Integer"
end

Answer 4

A more "duck typing" way is to use respond_to? this way "integer-like" or "string-like" classes can also be used

if(s.respond_to?(:match) && s.match(".com")){
  puts "It's a .com"
else
  puts "It's not"
end

Answer 5

To capitalize on the answer of Alex D, using refinements:

module CoreExtensions
  module Integerable
    refine String do
      def integer?
        Integer(self)
      rescue ArgumentError
        false
      else
        true
      end
    end
  end
end

Later, in you class:

require 'core_ext/string/integerable'

class MyClass
  using CoreExtensions::Integerable

  def method
    'my_string'.integer?
  end
end

Answer 6

I have had a similar issue before trying to determine if something is a string or any sort of number whatsoever. I have tried using a regular expression, but that is not reliable for my use case. Instead, you can check the variable's class to see if it is a descendant of the Numeric class.

if column.class < Numeric
  number_to_currency(column)
else
  column.html_safe
end

In this situation, you could also substitute for any of the Numeric descendants: BigDecimal, Date::Infinity, Integer, Fixnum, Float, Bignum, Rational, Complex