Ok / Err

Call .safe.call on any operation to get an Ok or Err result instead of a raised exception. The real payoff is pattern matching – you can destructure the outcome in a case/in block and handle each case cleanly.

Pattern matching

include Dex::Match

result = CreateUser.new(email: "alice@example.com").safe.call

case result
in Ok(name:, email:)
  puts "Welcome, #{name} (#{email})"
in Err(code: :email_taken)
  puts "Already registered"
in Err(code:, message:)
  puts "Error #{code}: #{message}"
end

Ok deconstructs by delegating to its value – if the value is a Hash or responds to deconstruct_keys, you can match its contents directly. Err deconstructs into { code:, message:, details: }.

Without Dex::Match, use the fully qualified names:

case result
in Dex::Ok
  # ...
in Dex::Err(code: :not_found)
  # ...
end

Ok

Returned when the operation succeeds. Wraps the return value.

result = CreateUser.new(email: "alice@example.com").safe.call

result.ok?     # => true
result.error?  # => false
result.value   # => the return value from perform
result.value!  # => same as .value (just returns it)

Ok delegates method calls to its value, so you can often use it directly:

result = FindUser.new(user_id: 1).safe.call
result.name   # => delegates to user.name
result.email  # => delegates to user.email

Err

Returned when the operation calls error! or a rescue_from mapping triggers. Wraps the Dex::Error.

result = CreateUser.new(email: "taken@example.com").safe.call

result.ok?      # => false
result.error?   # => true
result.value    # => nil
result.value!   # => raises the original Dex::Error
result.code     # => :email_taken
result.message  # => "This email is already in use"
result.details  # => nil or Hash

In controllers

def create
  result = CreateUser.new(params.permit(:email, :name).to_h).safe.call

  case result
  in Dex::Ok
    redirect_to result.value
  in Dex::Err(code: :email_taken)
    flash[:error] = result.message
    render :new
  end
end

Composing operations

user_result = CreateUser.new(email: email).safe.call
return if user_result.error?

SendWelcomeEmail.call(user_id: user_result.value.id)

For fire-and-forget calls where you just want exceptions to propagate, the regular .call is simpler.