How to return to the calling method?

Question

I have a program that uses a method for verification, if that verification failed I would like to return to the method it was called from, for example:

def obtain_pokemon_name
  print 'Enter Pokemon: '
  pokemon = gets.chomp.capitalize
  obtain_basic_attack(pokemon)
end

def obtain_basic_attack(poke)
  print 'Enter basic attack: '
  basic_attack = gets.chomp.downcase
  check_attacks(poke, basic_attack)
  obtain_spec_attack(poke)
end

def obtain_spec_attack(poke)
  print 'Enter special attack: '
  spec_attack = gets.chomp.downcase
  check_attacks(poke, spec_attack)
end

def check_attacks(pokemon, attack)
  if POKEMON_ATTACKS[pokemon][attack] == nil
    puts "#{attack} is not one of #{pokemon}'s attacks, try again.."
    return # to where this function was called
  else
    attack
  end
end

begin
  obtain_pokemon_name
rescue => e
  puts "Failed with error code: #{e}"
end

When this is run:

Enter Pokemon: arbok
Enter basic attack: eat
eat is not one of Arbok's attacks, try again..
Enter special attack: test
test is not one of Arbok's attacks, try again..

Attack list:

POKEMON_ATTACKS = {
    'Bulbasaur' => {'tackle' => 10.9, 'vine whip' => 15.4, 'power whip' => 21.4, 'seed bomb' => 12.5, 'sludge bomb' => 19.2},
    'Ivysaur' => {'razor leaf' => 10.3, 'vine whip' => 15.4, 'power whip' => 21.4, 'sludge bomb' => 19.2, 'solar beam' => 13.3},
    'Kakuna' => {'bug bite' => 13.3, 'poison sting' => 10.3, 'struggle' => 8.8},
    'Beedrill' => {'bug bite' => 13.3, 'poison jab' => 14.3, 'aerial ace' => 8.6, 'sludge bomb' => 19.2, 'x-scissor' => 14.3},
    'Pidgey' => {'quick attack' => 7.5, 'tackle' => 10.9, 'aerial ace' => 8.6, 'air cutter' => 7.6, 'twister' => 5.6},
    'Ekans' => {'acid' => 9.5, 'poison sting' => 10.3, 'gunk shot' => 20.0, 'sludge bomb' => 19.2, 'wrap' => 3.8},
    'Arbok' => {'acid' => 9.5, 'bite' => 12.0, 'dark pulse' => 12.9, 'gunk shot' => 20.0, 'sludge wave' => 17.6},
}

So my question is, if the attack is not present in the data, how can I return back to the calling method? So for instance if I call arbok and his attack is tackle if it doesn't exist in the hash, how would I return to the obtain_basic_attack(poke) method?

I suggest you take a look at recursion. Here's a good analogy: http://stackoverflow.com/questions/717725/understanding-recursion — Un3qual, Jul 29 '16 at 18:31

score 2 · Accepted Answer · edited Jul 29 '16 at 19:05

RIght here:

   puts "#{attack} is not one of #{pokemon}'s attacks, try again.."
    return # to where this function was called

you should call the original method again. i.e.

  if POKEMON_ATTACKS[pokemon][attack] == nil
    puts "#{attack} is not one of #{pokemon}'s attacks, try again.."
    return obtain_spec_attack(poke)

You could alternatively add this logic to obtain_spec_attack:

def obtain_spec_attack(poke)
  loop do
    print 'Enter special attack: '
    spec_attack = gets.chomp.downcase
    attack_found = check_attacks(poke, spec_attack)
    if attack_found
      break attack_found # this will return attack_found from the loop
    else
      puts "attack not found"
    end
  end
end

edit

looking at your question again, I realize you want to return to a method multiple levels up. You could use the approaches I've already outlined, or alternatively use rescue:

def obtain_basic_attack(poke)
  begin
    print 'Enter basic attack: '
    basic_attack = gets.chomp.downcase
    check_attacks(poke, basic_attack)
    obtain_spec_attack(poke)
  rescue AttackNotFoundError
    retry # runs the 'begin' block again
  end
end

def obtain_spec_attack(poke)
  print 'Enter special attack: '
  spec_attack = gets.chomp.downcase
  check_attacks(poke, spec_attack)
end

def check_attacks(pokemon, attack)
  if POKEMON_ATTACKS[pokemon][attack] == nil
    puts "#{attack} is not one of #{pokemon}'s attacks, try again.."
    raise AttackNotFoundError
  else
    attack
  end
end

In order to use a custom error like AttackNotFoundError, you need to define the error class somewhere:

class AttackNotFoundError < StandardError; end

You could use any error really, such as raise StandardError, but it's better to restrict what errors you're rescuing so that you don't accidentally rescue an unrelated error.

If you look at the code, there's more then one calling method. However the loop would probably work — Rubyist, Jul 29 '16 at 18:38
That's a genius idea!!! I didn't even think about rescue clauses, thank you so much! — Rubyist, Jul 29 '16 at 19:00
Sure, by the way something like `if POKEMON_ATTACKS[pokemon][attack] == nil` is usually unnecessary, you can probably remove the `== nil` and `if` will evaluate if it is truthy/falsy — max pleaner, Jul 29 '16 at 20:25
I can't decide whether this is an abuse of exceptions or not. Idiomatically, you would probably rather use `throw`/`catch` instead. — Jörg W Mittag, Jul 30 '16 at 01:33

How to return to the calling method?

1 Answers1