Inserting a value into an array under some condition

Question

How can I add value to an array inline under some condition?

This example:

["aaa", ("bbb" if false)]
# => ["aaa", nil]

adds nil, but, I do not want to add anything:

["aaa"]

Answer 1

You either do:

["aaa", ("bbb" if false)].compact

or:

["aaa", *("bbb" if false)]

But be careful with certain classes when you use the second option, as it may mess up objects of certain classes. For example, a hash would be converted into an array:

["aaa", *({b: :b} if true)]
# => ["aaa", [:b, :b]]

Answer 2

I would even post this as an answer since that’s a most succinct and clean way to accomplish this task.

["aaa"].tap { |arr| arr << "bbb" if false }

---

In more generic and easy to follow way:

input = [42]
to_add = {true: :true, false: :false}

to_add.each do |needed, value|
  input.tap { |arr| arr << value if needed }
end
#⇒ [42, :true]

Answer 3

You could concat an empty array when the condition is false, which essentially does nothing:

["aaa"] + (1==1 ? ["foo"] : [])
 => ["aaa", "foo"]
["aaa"] + (1==2 ? ["foo"] : [])
 => ["aaa"]