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 using eval?

Maybe something with regex..?

Answer 1

You must either or eval it, or parse it; and since you don't want to eval:

mathstring = '3+3'
i, op, j = mathstring.scan(/(\d+)([+\-*\/])(\d+)/)[0] #=> ["3", "+", "3"]
i.to_i.send op, j.to_i #=> 6

If you want to implement more complex stuff you could use RubyParser (as @LBg wrote here - you could look at other answers too)

Answer 2

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