CODEWITHSUNDEEP
rubyfunctionrecursion
Alex
Alex

Reputation: 23

Ruby recursive function

I've problem returning value from recursive function. 

def ask_question(question)
    print question
    answer = STDIN.gets.chomp

    ask_question question if answer.empty?
    return answer
end

The first time the answer is returned properly but I got empty string in next calls. Why is that?

Upvotes: 2

Views: 8849

Answers (2)

tokland
tokland

Reputation: 67900

Your code does not work because the variable answer you return it's always the one in the first iteration (each call has its own local scope). So a possible solution is:

def ask_question(question)
    print question
    answer = STDIN.gets.chomp
    answer.empty? ? ask_question(question) : answer
end

Note though that this recursive construction is fine with languages that support tail-call optimization, but Ruby does not force it, so it will usually create a new stack frame for each iteration and eventually it will blow. I'd recommend looping, for example: 

def ask_question(question)
  loop do 
    print question
    answer = STDIN.gets.chomp
    break answer unless answer.empty?
  end
end

Upvotes: 1

Jeremy
Jeremy

Reputation: 22435

That is because you aren't returning the value returned by your recursive calls to ask_question.

def ask_question(question)
    print question
    answer = STDIN.gets.chomp
    answer = ask_question question if answer.empty?
    return answer;
end

All you were doing is returning the first user input value (in your case an empty string) when the method was done.

Upvotes: 7

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