Why does '||' operator return '[ ]'?

Question

I tested this on console:

[] || 1 # => []

Shouldn't it return the value that exits, and not [] ? I can change it to ternary operator, which works fine, but why does the condition above not work?

Answer 1

Because [] is truthy value in Ruby, so the second part of your expression is never executed, it always evaluates to [] . In Ruby, just false and nil aren't truthy.

Oh, anyway, you don't need that. map returns an empty array if the array is empty.

Model.new(
  name: abc.name,
  description: abc.description,
  product_ids: abc.product_ids.map(&:id) 
)

Answer 2

The exact semantics of || are:

1. if first expression is not nil or false , return it
2. if first expression is nil or false , return the second expression

So since [] is truthy it will evaluate to [] , as explained by @Ursus.