FAQ: The Zen of Ruby - One Good Turn Deserves a Ternary

[wiki-bot]

This community-built FAQ covers the “One Good Turn Deserves a Ternary” exercise from the lesson “The Zen of Ruby”.

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FAQs on the exercise One Good Turn Deserves a Ternary

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[dcts]

I just started using ternary if/else statements. Im a bit confused why the condition is printed to the command line as 15 (if true) or 16 (if false). Here a short code:

def do_if_true
  puts "TRUE!!"
end

def do_if_false
  puts "FALSE!!"
end

condition = 3<4
puts condition ? do_if_true : do_if_false

# output in codecademy editor: // TRUE!!
#                              // 15
# output running in atom:      // TRUE!!

EDIT: as pointed out above the output differs depending on where i run the code (webinterface from codecademy vs atom runner). Im just curious why in the codecademy editor i got a second line printing out 15.

[mtf]

It would appear connected somehow to the fact that you are puts-ing the puts in the functions.

def do_if_true
  "TRUE!!"
end

def do_if_false
  "FALSE!!"
end

condition = 3 < 4
puts condition ? do_if_true : do_if_false

One can only speculate where the numbers are derived. That’s a puzzler.

[dcts]

ah i just realized that i misunderstood how the ternary syntax works… sorry my code was strange! I was expecting to get the outcome of the condition checking back from the ternary one linerer, and thought that the code after the “?” and after the “:” just gets executed (depending on the condition), whereas whats written there actually is returned! Thanks for your help again!

[mtf]

The returns are on your methods. In Ruby they are implicit. All puts does is print the expression resulting in the ternary. The ternary doesn’t return anything. It’s a control flow device.

[mlang0608]

puts 3 < 4 ? “3 is less than 4!” : “3 is not less than 4.”

I am wondering why puts must be in the beginning and the following does not work:

3 > 4 ? puts “3 is less than 4!” : puts “3 is not less than 4.”

[mtf]

It may go to methodology.

def do_if_true
  "TRUE!!"
end

def do_if_false
  "FALSE!!"
end

condition = 3 < 4
puts condition ? do_if_true : do_if_false

There is no repetition of common methods, and isolation of exclusive methods.

Consider,

stdout << expression

vs.,

condition ? stdout << string expression : stdout << string expression

[jennajlee92]

Why do we put “puts” in front of the condition and not within the body?

[mtf]

Because the body is comprised of two segments in the form of an expression. One outcome or the other is the value that is sent to puts.

a = rand(10)
b = rand(10)
puts a > b ? 1 : a < b ? -1 : 0

The above is a nested ternary. The outcome can be either, 1, -1, or 0.

Note how redundant the following would be by comparison:

a > b ? puts 1 : a < b ? puts -1 : puts 0

Clearly it makes perfect sense to evaluate the expression, first, and puts the final outcome.