The document discusses the importance of use cases in code. It provides an example use case class for playing a team game that defines roles, algorithms, and domain objects without mentioning the GUI, persistence, or external API calls. The goal is clean use case code, and aspects like the GUI and persistence can be handled separately through aspect-oriented programming and dependency injection of roles at runtime.

1. Use cases
are
important
Andrzej Krzywda

2. Use cases
in the code
are
even more
important

3. class PlayTeamGameUseCase
constructor: (@game, @player) ->
Role(@player, PlayerWithFriends)
Role(@game, TeamCompetition)
tryToEnterGameArea: () =>
if @amIEnteringGameFirstTime()
if @amICommingFromInvitation()
@tellPlayerHeIsPartOfTeam()
@teachPlayerHowToPlay()
else #n-th time...
if @amICommingFromInvitation()
@tellPlayerHeIsPartOfTeam()
if @haveNotYetPickedFavPizzaCountry()
@askPlayerToDeclareHisFavPizzaCountry()
(more methods here)

4. Name
class PlayTeamGameUseCase
constructor: (@game, @player) ->
Role(@player, PlayerWithFriends)
Role(@game, TeamCompetition)
tryToEnterGameArea: () =>
if @amIEnteringGameFirstTime()
if @amICommingFromInvitation()
@tellPlayerHeIsPartOfTeam()
@teachPlayerHowToPlay()
else #n-th time...
if @amICommingFromInvitation()
@tellPlayerHeIsPartOfTeam()
if @haveNotYetPickedFavPizzaCountry()
@askPlayerToDeclareHisFavPizzaCountry()
(more methods here)

5. Name
class PlayTeamGameUseCase
constructor: (@game, @player) -> Actors
Role(@player, PlayerWithFriends)
Role(@game, TeamCompetition)
tryToEnterGameArea: () =>
if @amIEnteringGameFirstTime()
if @amICommingFromInvitation()
@tellPlayerHeIsPartOfTeam()
@teachPlayerHowToPlay()
else #n-th time...
if @amICommingFromInvitation()
@tellPlayerHeIsPartOfTeam()
if @haveNotYetPickedFavPizzaCountry()
@askPlayerToDeclareHisFavPizzaCountry()
(more methods here)

6. Name
class PlayTeamGameUseCase
constructor: (@game, @player) -> Actors
Role(@player, PlayerWithFriends)
Role(@game, TeamCompetition) Roles
tryToEnterGameArea: () =>
if @amIEnteringGameFirstTime()
if @amICommingFromInvitation()
@tellPlayerHeIsPartOfTeam()
@teachPlayerHowToPlay()
else #n-th time...
if @amICommingFromInvitation()
@tellPlayerHeIsPartOfTeam()
if @haveNotYetPickedFavPizzaCountry()
@askPlayerToDeclareHisFavPizzaCountry()
(more methods here)

7. Name
class PlayTeamGameUseCase
constructor: (@game, @player) -> Actors
Role(@player, PlayerWithFriends)
Role(@game, TeamCompetition) Roles
tryToEnterGameArea: () =>
if @amIEnteringGameFirstTime()
if @amICommingFromInvitation()
@tellPlayerHeIsPartOfTeam()
@teachPlayerHowToPlay() Algorithm
else #n-th time...
if @amICommingFromInvitation()
@tellPlayerHeIsPartOfTeam()
if @haveNotYetPickedFavPizzaCountry()
@askPlayerToDeclareHisFavPizzaCountry()
(more methods here)

8. Name
class PlayTeamGameUseCase
constructor: (@game, @player) -> Actors
Role(@player, PlayerWithFriends)
Role(@game, TeamCompetition) Roles
tryToEnterGameArea: () =>
if @amIEnteringGameFirstTime()
if @amICommingFromInvitation()
@tellPlayerHeIsPartOfTeam()
@teachPlayerHowToPlay() Algorithm
else #n-th time...
if @amICommingFromInvitation()
@tellPlayerHeIsPartOfTeam()
uses domain objects
if @haveNotYetPickedFavPizzaCountry()
@askPlayerToDeclareHisFavPizzaCountry()
(more methods here)

9. Name
class PlayTeamGameUseCase
constructor: (@game, @player) -> Actors
Role(@player, PlayerWithFriends)
Role(@game, TeamCompetition) Roles
tryToEnterGameArea: () =>
if @amIEnteringGameFirstTime()
if @amICommingFromInvitation()
@tellPlayerHeIsPartOfTeam()
@teachPlayerHowToPlay() Algorithm
else #n-th time...
if @amICommingFromInvitation()
@tellPlayerHeIsPartOfTeam()
uses domain objects
if @haveNotYetPickedFavPizzaCountry()
@askPlayerToDeclareHisFavPizzaCountry()
(more methods here) Nothing about GUI or persistence!

10. Where is?
• GUI
• Persistence
• API calls
• events

11. A clean use case code
is the main goal

12. AOP + DCI

13. Aspect Oriented
Programming

14. AOP gives us
method hooks

15. After, Before, Around

16. GUI & persistence

17. class GameUseCaseGlue
constructor: (@gameUseCase, @game, @gui) ->
execute: () =>
Around(@gameUseCase, 'tryToEnterGameArea', @checkFbInvitation)
After (@gameUseCase, 'tryToEnterGameArea', @showTeamArea)
After (@gameUseCase, 'tryToEnterGameArea', @showButtonInviteOrPostPicture)
Around(@gameUseCase, 'tellPlayerHeIsPartOfTeam', @showTeamPopup)
Around(@gameUseCase, 'askPlayerToLikeFanpage', @showLikePopup)
Around(@gameUseCase, 'teachPlayerHowToPlay', @showTutorialPopup)
Around(@gameUseCase, 'playerWantsToKnowWinnersWithPrize', @showWinnersPopup)
Around(@gameUseCase, 'playerWantsToKnowPrizes', @showPrizesPopup)
Around(@gameUseCase, 'askPlayerToDeclareHisFavCountry', @showDeclareCountryPopup)
Around(@gameUseCase, 'iAcceptMyFriendInvitationToATeam', @onIAcceptMyFriendInvitationToATeam)
Around(@gui, 'inviteClicked', @inviteFriends) # gameUseCase.inviteFriends
Around(@gameUseCase, 'inviteFriends', @storeInvitationInTheDB) DB here
Glue code

18. Around(@gameUseCase, 'tellPlayerHeIsPartOfTeam', @showTeamPopup)

19. (still glue code)
showTeamPopup: (proceed, friendsInviting) =>
data = {inviting_friends: friendsInviting}
popup = @popupsComponent.showPopup('team_popup', data)
popup.onClose => proceed(friendsInviting))

20. DCI

21. class PlayTeamGameUseCase Use case == context
constructor: (@game, @player) ->
Role(@player, PlayerWithFriends)
Role(@game, TeamCompetition) Roles injected runtime
tryToEnterGameArea: () =>
if @amIEnteringGameFirstTime()
if @amICommingFromInvitation()
@tellPlayerHeIsPartOfTeam()
data objects interact with
@teachPlayerHowToPlay()
each other
else #n-th time...
if @amICommingFromInvitation()
@tellPlayerHeIsPartOfTeam()
if @haveNotYetPickedFavPizzaCountry()
@askPlayerToDeclareHisFavPizzaCountry()
(more methods here)

22. class PlayerWithFriends
setup: => a role
@friends = []
@invitedFriends = []
@acceptedFriends = []
setInvitedFriends: (facebookUids) =>
for facebookUid in facebookUids
friend = new Friend({facebookUid: facebookUid})
@invitedFriends.push(friend)
setFriends: (friends) =>
@friends = friends
addFriend: (friend) =>
existing = @getFriendByFacebookUid(friend?.facebookUid)
if not existing?
@friends.push(friend)

23. not only for
Single Page Applications

24. What use cases are in
your project?

25. learn more about AOP and DCI and ...
Enjoy writing
elegant
use cases!