Question

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

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.

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…

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.

Answer 1

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

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:

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