Ruby evaluate without eval?

Question

How could I evaluate at mathematical string without using eval?

Example:

mathstring = \"3+3\"

Anyway that can be evaluated without

Answer 1

I'm assuming you don't want to use eval because of security reasons, and it is indeed very hard to properly sanitize input for eval, but for simple mathematical expressions perhaps you could just check that it only includes mathematical operators and numbers?

mathstring = "3+3"
puts mathstring[/\A[\d+\-*\/=. ]+\z/] ? eval(mathstring) : "Invalid expression"
=> 6