Ruby conditional branch. if, conditional operator (ternary operator), unless, case

Boolean value in Ruby

In Ruby, only false or nil is false, and everything else is true, including 0 and the empty string.

if If the conditional expression is matched, the specified process is performed.

syntax

if expression[then]
formula...
[elsif expression[then]
formula... ]
...
[else
formula... ]
end

[] Is an optional part.

Be careful if you have experience with other languages because it is elsif (without e) instead of els ** e ** if. The last els ** e ** requires e.

Example sentence

score = 90

if score == 100
  puts 'S'
elsif score >= 90
  puts 'A'
elsif score >= 80
  puts 'B'
else
  puts 'C'
end

#Example using then
if score == 100 then
  puts 'S'
end

Conditional operator (ternary operator)

Demonstrates its power when judgment conditions and processing are short! It will be easier to see.

syntax

Equation 1?Equation 2:Equation 3
#conditions?In case of ◯:In case of ×

Example sentence

checked = true
puts checked ? "Already" : "Not yet"

#Same meaning as the following sentence.
# puts (if checked then  "Already" else "Not yet" end)

unless

Opposite to if. If not. Sentences that can be written with unless can also be written with if, so you can write as you like.

Note that it becomes difficult to understand if it becomes a double negation. Unless and code readability in Ruby | TechRacho-Engineer's "?" To "!"-| BPS Co., Ltd.

syntax

There is no elsif. else can be omitted.

unless expression[then]
formula...
[else
formula... ]
end

Example sentence

unless baby?
  #Conditional expression is false(false)In the case of
  puts "eat rice"
else
  puts "Drink milk"
end

case As a guideline for proper use with if, I think that case is more suitable for parallel conditions, but how about it?

I thought it was the same as the switch statement, but it seems to be strictly different ... [I would like to say a few words to those who think that the Ruby case is a switch statement of 〇〇 (language name)](https://melborne.github.io/2013/02/25/i- wanna-say-something-about-rubys-case /)

syntax

case [formula]
[when expression[,formula] ...[, `*'formula] [then]
formula..]..
[when `*'formula[then]
formula..]..
[else
formula..]
end

Example sentence

os = "macOS"

case os
when "Windows"
  #processing
when "macOS", "Unix"
  #Conditions for performing the same processing can be described together
when "Linux"
  #processing
else
  #processing
end

reference

Control Structure (Ruby 2.7.0 Reference Manual) Operator expression (Ruby 2.7.0 reference manual)