Add A Basic Case Statement as a Ruby til

ruby/a-basic-case-statement.md

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+# A Basic Case Statement
+
+The syntax for case statements (or switch statements) is a little different for
+each language. I often confuse the Ruby and JavaScript syntax or wonder if I
+need to be using a colon anywhere.
+
+Here is a demonstration of how to write a basic case statement in Ruby.
+
+```ruby
+case ['taco', 'burrito', 'pizza', nil].sample
+when 'taco'
+  puts 'Taco, eh. Carne asada or al pastor?'
+when 'burrito'
+  puts 'Burrito, eh. Want it smothered?'
+when 'pizza'
+  puts 'Pizza, eh. Cheese or pepperoni?'
+else
+  puts 'What do you want to eat?'
+end
+```
+
+This next example demonstrates two things. First, you can make things terser
+with the `then` syntax. Second, the case statement does an implicit return of
+whatever the last value is from the evaluated case. So it can be used as part
+of a variable assignment.
+
+```ruby
+question =
+  case ['taco', 'burrito', 'pizza', nil].sample
+  when 'taco' then 'Taco, eh. Carne asada or al pastor?'
+  when 'burrito' then 'Burrito, eh. Want it smothered?'
+  when 'pizza' then 'Pizza, eh. Cheese or pepperoni?'
+  else 'What do you want to eat?'
+  end
+
+puts question
+```