Unit
Some constructors do not require you to pass a value. As a default they use Unit, a special singleton value:
extend Dry::Monads[:result]
Success().value! # => Unit
Unit doesn't have any special properties or methods, it's similar to nil except for it is not i.e. if Unit passes.
Unit is usually excluded from the output:
extend Dry::Monads[:result]
# Outputs as "Success()" but technically it's "Success(Unit)"
Success()
Discarding values
When the outcome of an operation is not a caller's concern, call .discard, it will map the wrapped value to Unit:
extend Dry::Monads[:result]
result = create_user # returns Success(#<User...>) or Failure(...)
result.discard # => Maps Success(#<User ...>) to Success() but leaves Failure(...) intact