How to turn a Msg into a Cmd Msg?

Only Use Sparsely: Better split the update function into multiple smaller functions.
Problem
Solution
Alternative Solution
type Msg =
  LoginSucceeded User
  | InfoMessage String
  
update : Msg -> Model -> (Model, Cmd Msg)
update msg model =
  case msg of
    LoginSucceeded newUser ->
      ( { model | currentUser = newUser }
      , Cmd.none
      )
    InfoMessage message ->
      ( { model | message = Just message }
      , Cmd.none
      )
type Msg =
  LoginSucceeded User
  | InfoMessage String
  
update : Msg -> Model -> (Model, Cmd Msg)
update msg model =
  case msg of
    LoginSucceeded newUser ->
      ( { model | currentUser = newUser }
      , sendMsg <| InfoMessage "Login Successful"
      )
    InfoMessage message ->
      ( { model | message = Just message }
      , Cmd.none
      )
​
sendMsg : msg -> Cmd msg
sendMsg msg =
  Task.succeed msg
  |> Task.perform identity
type Msg =
  LoginSucceeded User
  | InfoMessage String
  
update : Msg -> Model -> (Model, Cmd Msg)
update msg model =
  case msg of
    LoginSucceeded newUser ->
      ( model
        |> updateUser newUser
        |> updateMessage "Login Successful"
      , Cmd.none
      )
    InfoMessage message ->
      ( model |> updateMessage message
      , Cmd.none
      )
​
updateUser : User -> Model -> Model
updateUser user model =
  { model | currentUser = user }
​
updateMessage : String -> Model -> Model
updateMessage message model =
  { model | message = Just message }
This is the a better solution
Question
How can I display a Message after a user logged in?
Answer
Use the following function:
sendMsg : msg -> Cmd msg
sendMsg msg =
  Task.succeed msg
  |> Task.perform identity
Further reading
📄Article: How to turn a Msg into a Cmd Msg in Elm? by Wouter In t Velt

Frequently asked questions - Previous

How to structure an Elm project?

Next - Frequently asked questions

How to update nested Records?

Last modified 2yr ago

Copy link

Outline

Question

Answer