what is the meaning in if #(x =~ /\d/).nil? #return the index of the non-digit ? I quite don't get it

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Ruby

input = ARGV 
 
class RPNCalculator
 
    def evaluate(expression)
        to_evaluate = []
        a = expression.split(" ")
        a.each do |x|
            if (x =~ /\d/).nil? #return the index of the non-digit
                to_count = to_evaluate.pop(2)
                to_evaluate << to_count[0].send(x, to_count[1])
            else
                to_evaluate << x.to_i
            end
        end
        to_evaluate[0]
    end
end
 
 
calc = RPNCalculator.new
p calc.evaluate(input)

Posted 13-May-15 2:28am

Member 11687521

Updated 13-May-15 2:36am

Thomas Daniels

v2

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Thomas Daniels · Answer 1 · 2015-05-13T02:59:00

That expression evaluates to true if the char is not a digit.

x =~ /\d/ runs the regular expression[^] \d on the char: if there is a digit in the string (which is, in this case, only 1 char), this expression returns the index of the digit. If it does not contain a digit, it returns nil.

.nil? checks whether x =~ /\d/ equals nil. If it does, it returns true. If it does not, it returns false.