Using boolean operators in a "case... when" statement (Ruby)

Question

I'm trying to write a method that takes the user's input and checks it for validity. It's in a "case...when" statement. This part checks that the user has entered a Y or N only.

when 3
    input = gets.chomp.to_s.downcase
    unless input (=="y") || (=="n")
        puts "That is not a valid choice. Please enter Y or N."
        get_input(text, 3)
    end

The compiler doesn't like my boolean statement and I'm not sure why. It tells me "syntax error, unexpected [x]" and points to various parts of the statement. Pretty much tearing my hair out here... am I doing something obvious wrong?

One of the requirements for questions about code you wrote is you provide an example that is usable: "Questions concerning problems with code you've written must describe the specific problem — and include valid code to reproduce it — in the question itself." Saying "points to various parts of the statement" doesn't help at all. — the Tin Man
– the Tin Man, Commented Sep 18, 2013 at 1:28

Marcelo De Polli · Accepted Answer · 2013-09-18 01:32:16Z

4

Try this:

unless ['y', 'n'].include?(input)

answered Sep 18, 2013 at 1:32

Marcelo De Polli

29.4k4 gold badges41 silver badges47 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Hauleth Over a year ago

The best answer IMHO.

the Tin Man · Accepted Answer · 2013-09-18 01:36:03Z

2

Depending on the language(s) you come from, you might find one of these different ways more appealing. You could write:

 unless input (=="y") || (=="n")

As:

if !input[/^[yn]$/]
    puts "That is not a valid choice. Please enter Y or N."
    get_input(text, 3)
end

Or:

unless input[/^[yn]$/]
  ...
end

Or:

unless (input == 'y' || input == 'n')
  ...
end

Or:

case input
when 'y', 'n'
  ...
else
  puts "That is not a valid choice. Please enter Y or N."
  get_input(text, 3)
end

answered Sep 18, 2013 at 1:36

the Tin Man

161k44 gold badges222 silver badges308 bronze badges

Comments

Michael Durrant · Accepted Answer · 2013-09-18 01:44:35Z

1

I find the unless first does not read well. Starting off with a negative would be fairly ok here but in more complicated conditionals it loses readability.

I personally prefer

$ if q !~ /[yn]/ # Does NOT match pattern
$   puts "That is not a valid choice. Please enter Y or N."
$   get_input(text, 3)    
$ end

for maximum easy readability by all.

answered Sep 18, 2013 at 1:44

Michael Durrant

97.2k102 gold badges352 silver badges536 bronze badges

Comments

Stefan · Accepted Answer · 2013-09-18 08:33:04Z

0

Besides getting the condition right, there seems to be a recursion in your method. I suspect your method looks like this:

def get_input(text, option)
  # ...
  case option
  when 1
    # ...
  when 2
    # ...
  when 3
    unless condition
      puts "That is not a valid choice. Please enter Y or N."
      get_input(text, 3) # <- recursion!
    end
  end
  # ...
end

It would be better to use a loop here. Something like this:

def get_input(text, option)
  # ...
  case option
  when 3
    loop do
      valid = case gets.chomp
              when /^(y|yes)$/i
                puts "positive input"
                true
              when /^(n|no)$/i
                puts "negative input"
                true
              else
                puts "That is not a valid choice. Please enter Y or N."
                false
              end
      break if valid
    end
  end
end

The input is checked with another case statement. If the input is valid (i.e. y or n), true is returned and break exits the loop, otherwise false is returned, break is not called and the loops starts over again.

BTW, (y|yes) matches y and yes, (n|no) matches n and no, ^...$ ensures that there's nothing before or after, and the i makes it case insensitive.

So /^(n|no)$/i matches n, N, no, No, nO, and NO.

answered Sep 18, 2013 at 8:33

Stefan

115k14 gold badges157 silver badges234 bronze badges

2 Comments

the Tin Man Over a year ago

/^no?$/i would work as would /^y(es)?$/i. Using the non-capturing form ((?:es)?) is more proper, but wasted energy for this task.

Stefan Over a year ago

Yes, but it would take me a second to understand what /^no?$/ is actually matching. Using alternation makes the regex very explicit and allows to add other values easily, e.g. /^(y|yes|ok)$/

Collectives™ on Stack Overflow

Using boolean operators in a "case... when" statement (Ruby)

4 Answers 4

1 Comment

Comments

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

1 Comment

Comments

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related