0 to 100% Kotlin @ Trafi

Tools, patterns and benefits that we discovered migrating to a 100% Kotlin Android codebase at Trafi.

Kotlin's features that make our team more productive:
- Conciseness maintains focus
- Extension functions keep logic in scope
- Sealed class hierarchies express state
- Functional constructs encourage better code
- Explicit mutability forces design
- Explicit nullability forces design

Presented at GDG Vilnius.
https://www.meetup.com/GDG-Vilnius/events/252862364/

Transcript

1. 0 to 100% Kotlin @ Well.. almost ;)
2. Part 1: A story of models
3. public class Ticket { public String id; public String name; @Nullable public Date endTime; public Ticket(String id, String name, @Nullable Date endTime) { this.id = id; this.name = name; this.endTime = endTime; } }
4. public class Ticket { @SerializedName("Id") public String id; @SerializedName("Name") public String name; @SerializedName("EndTime") @Nullable public Date endTime; public Ticket(String id, String name, @Nullable Date endTime) { this.id = id; this.name = name; this.endTime = endTime; } }
5. public class Ticket { @SerializedName("Id") public String id; @SerializedName("Name") public String name; @SerializedName("EndTime") @Nullable public Date endTime; public Ticket(String id, String name, @Nullable Date endTime) { this.id = id; this.name = name; this.endTime = endTime; } }
6. public class Ticket { @SerializedName("Id") public String id; @SerializedName("Name") public String name; @SerializedName("EndTime") @Nullable public Date endTime; public Ticket(String id, String name, @Nullable Date endTime) { this.id = id; this.name = name; this.endTime = endTime; } @Override public boolean equals(Object o) { if (this == o) return true; if (o == null || getClass() != o.getClass()) return false; Ticket ticket = (Ticket) o; if (!id.equals(ticket.id)) return false; if (!name.equals(ticket.name)) return false;
7. // .. public boolean equals(Object o) { if (this == o) return true; if (o == null || getClass() != o.getClass()) return false; Ticket ticket = (Ticket) o; if (!id.equals(ticket.id)) return false; if (!name.equals(ticket.name)) return false; return endTime != null ? endTime.equals(ticket.endTime) : ticket.endTime == null; } @Override public int hashCode() { int result = id.hashCode(); result = 31 * result + name.hashCode(); result = 31 * result + (endTime != null ? endTime.hashCode() : 0); return result; } }
8. public class Ticket { @SerializedName("Id") public String id; @SerializedName("Name") public String name; @SerializedName("EndTime") @Nullable public Date endTime; public Ticket(String id, String name, @Nullable Date endTime) { this.id = id; this.name = name; this.endTime = endTime; } @Override public boolean equals(Object o) { if (this == o) return true; if (o == null || getClass() != o.getClass()) return false; Ticket ticket = (Ticket) o; if (!id.equals(ticket.id)) return false; if (!name.equals(ticket.name)) return false;
9. public class Ticket implements Parcelable { @SerializedName("Id") public String id; @SerializedName("Name") public String name; @SerializedName("EndTime") @Nullable public Date endTime; public Ticket(String id, String name, @Nullable Date endTime) { this.id = id; this.name = name; this.endTime = endTime; } protected Ticket(Parcel in) { id = in.readString(); name = in.readString(); if (in.readByte() == 0) { endTime = null; } else { endTime = new Date(in.readLong()); } }
10. // .. protected Ticket(Parcel in) { id = in.readString(); name = in.readString(); if (in.readByte() == 0) { endTime = null; } else { endTime = new Date(in.readLong()); } } @Override public void writeToParcel(Parcel dest, int flags) { dest.writeString(id); dest.writeString(name); if (endTime == null) { dest.writeByte((byte) 0); } else { dest.writeByte((byte) 1); dest.writeLong(endTime.getTime()); }
11. // .. @Override public void writeToParcel(Parcel dest, int flags) { dest.writeString(id); dest.writeString(name); if (endTime == null) { dest.writeByte((byte) 0); } else { dest.writeByte((byte) 1); dest.writeLong(endTime.getTime()); } } @Override public int describeContents() { return 0; } public static final Creator<Ticket> CREATOR = new Creator<Ticket>() { @Override public Ticket createFromParcel(Parcel in) {
12. // .. public static final Creator<Ticket> CREATOR = new Creator<Ticket>() { @Override public Ticket createFromParcel(Parcel in) { return new Ticket(in); } @Override public Ticket[] newArray(int size) { return new Ticket[size]; } }; @Override public boolean equals(Object o) { if (this == o) return true; if (o == null || getClass() != o.getClass()) return false; Ticket ticket = (Ticket) o; if (!id.equals(ticket.id)) return false;
13. // .. public boolean equals(Object o) { if (this == o) return true; if (o == null || getClass() != o.getClass()) return false; Ticket ticket = (Ticket) o; if (!id.equals(ticket.id)) return false; if (!name.equals(ticket.name)) return false; return endTime != null ? endTime.equals(ticket.endTime) : ticket.endTime == null; } @Override public int hashCode() { int result = id.hashCode(); result = 31 * result + name.hashCode(); result = 31 * result + (endTime != null ? endTime.hashCode() : 0); return result; } }
14. public class Ticket implements Parcelable { @SerializedName("Id") public String id; @SerializedName("Name") public String name; @SerializedName("EndTime") @Nullable public Date endTime; public Ticket(String id, String name, @Nullable Date endTime) { this.id = id; this.name = name; this.endTime = endTime; } protected Ticket(Parcel in) { id = in.readString(); name = in.readString(); if (in.readByte() == 0) { endTime = null; } else { endTime = new Date(in.readLong()); } }
15. can this be done automatically?
16. auto-value
17. auto-value github.com/google/auto
18. @AutoValue public abstract class Ticket { public abstract String getId(); public abstract String getName(); @Nullable public abstract Date getEndTime(); public static Ticket create(String id, String name, @Nullable Date endTime) { return new AutoValue_Ticket(id, name, endTime); } }
19. @AutoValue public abstract class Ticket { @SerializedName("Id") public abstract String getId(); @SerializedName("Name") public abstract String getName(); @Nullable @SerializedName("EndTime") public abstract Date getEndTime(); public static Ticket create(String id, String name, @Nullable Date endTime) { return new AutoValue_Ticket(id, name, endTime); } }
20. @AutoValue public abstract class Ticket { @SerializedName("Id") public abstract String getId(); @SerializedName("Name") public abstract String getName(); @Nullable @SerializedName("EndTime") public abstract Date getEndTime(); public static Ticket create(String id, String name, @Nullable Date endTime) { return new AutoValue_Ticket(id, name, endTime); } }
21. @AutoValue public abstract class Ticket { @SerializedName("Id") public abstract String getId(); @SerializedName("Name") public abstract String getName(); @Nullable @SerializedName("EndTime") public abstract Date getEndTime(); public static Ticket create(String id, String name, @Nullable Date endTime) { return new AutoValue_Ticket(id, name, endTime); } public static TypeAdapter<ActiveTicket> typeAdapter(Gson gson) { return new AutoValue_Ticket.GsonTypeAdapter(gson); } }
22. @AutoValue public abstract class Ticket { @SerializedName("Id") public abstract String getId(); @SerializedName("Name") public abstract String getName(); @Nullable @SerializedName("EndTime") public abstract Date getEndTime(); public static Ticket create(String id, String name, @Nullable Date endTime) { return new AutoValue_Ticket(id, name, endTime); } public static TypeAdapter<ActiveTicket> typeAdapter(Gson gson) { return new AutoValue_Ticket.GsonTypeAdapter(gson); } }
23. @AutoValue public abstract class Ticket implements Parcelable { @SerializedName("Id") public abstract String getId(); @SerializedName("Name") public abstract String getName(); @Nullable @SerializedName("EndTime") public abstract Date getEndTime(); public static Ticket create(String id, String name, @Nullable Date endTime) { return new AutoValue_Ticket(id, name, endTime); } public static TypeAdapter<ActiveTicket> typeAdapter(Gson gson) { return new AutoValue_Ticket.GsonTypeAdapter(gson); } }
24. @AutoValue public abstract class Ticket implements Parcelable { @SerializedName("Id") public abstract String getId(); @SerializedName("Name") public abstract String getName(); @Nullable @SerializedName("EndTime") public abstract Date getEndTime(); public static Ticket create(String id, String name, @Nullable Date endTime) { return new AutoValue_Ticket(id, name, endTime); } public static TypeAdapter<ActiveTicket> typeAdapter(Gson gson) { return new AutoValue_Ticket.GsonTypeAdapter(gson); } }
25. what is actually important?
26. public class Ticket { public String id; public String name; @Nullable public Date endTime; }
27. data class Ticket( val id: String, val name: String, val endTime: Date? = null )
28. data class Ticket( val id: String, val name: String, val endTime: Date? = null )
29. @JsonClass(generateAdapter = true) data class Ticket( @Json(name = "Id") val id: String, @Json(name = "Name") val name: String, @Json(name = "EndTime") val endTime: Date? = null )
30. @JsonClass(generateAdapter = true) data class Ticket( @Json(name = "Id") val id: String, @Json(name = "Name") val name: String, @Json(name = "EndTime") val endTime: Date? = null )
31. moshi
32. moshi github.com/square/moshi
33. @JsonClass(generateAdapter = true) data class Ticket( @Json(name = "Id") val id: String, @Json(name = "Name") val name: String, @Json(name = "EndTime") val endTime: Date? = null )
34. @Parcelize @JsonClass(generateAdapter = true) data class Ticket( @Json(name = "Id") val id: String, @Json(name = "Name") val name: String, @Json(name = "EndTime") val endTime: Date? = null ) : Parcelable
35. @Parcelize @JsonClass(generateAdapter = true) data class Ticket( @Json(name = "Id") val id: String, @Json(name = "Name") val name: String, @Json(name = "EndTime") val endTime: Date? = null ) : Parcelable
36. data class Ticket( val id: String, val name: String, val endTime: Date? = null )
37. @Parcelize @JsonClass(generateAdapter = true) data class Ticket( @Json(name = "Id") val id: String, @Json(name = "Name") val name: String, @Json(name = "EndTime") val endTime: Date? = null ) : Parcelable
38. val ticket = Ticket("a", "30 min")
39. val ticket = Ticket("a", "30 min") println(ticket.toString()) // Ticket(id=a, name=30 min, endTime=null)
40. val ticket = Ticket("a", "30 min") println(ticket.toString()) // Ticket(id=a, name=30 min, endTime=null) println(ticket.hashCode()) // -574755854
41. val ticket = Ticket("a", "30 min") println(ticket.toString()) // Ticket(id=a, name=30 min, endTime=null) println(ticket.hashCode()) // -574755854 val otherTicket = ticket.copy(endTime = Date(0))
42. val ticket = Ticket("a", "30 min") println(ticket.toString()) // Ticket(id=a, name=30 min, endTime=null) println(ticket.hashCode()) // -574755854 val otherTicket = ticket.copy(endTime = Date(0)) println(ticket == otherTicket) // false
43. val ticket = Ticket("a", "30 min") println(ticket.toString()) // Ticket(id=a, name=30 min, endTime=null) println(ticket.hashCode()) // -574755854 val otherTicket = ticket.copy(endTime = Date(0)) println(ticket == otherTicket) // false
44. Conciseness maintains focus
45. data class Ticket( val id: String, val name: String, val endTime: Date? = null )
46. data class Ticket( val id: String, val name: String, val endTime: Date? = null ) { val isValid: Boolean get() = endTime != null }
47. data class Ticket( val id: String, val name: String, val endTime: Date? = null )
48. data class Ticket( val id: String, val name: String, val endTime: Date? = null ) fun isValid(ticket: Ticket): Boolean { return ticket.endTime != null }
49. data class Ticket( val id: String, val name: String, val endTime: Date? = null ) fun Ticket.isValid(): Boolean { return ticket.endTime != null }
50. data class Ticket( val id: String, val name: String, val endTime: Date? = null ) fun Ticket.isValid(): Boolean { return endTime != null }
51. data class Ticket( val id: String, val name: String, val endTime: Date? = null ) fun Ticket.isValid(): Boolean { return endTime != null }
52. data class Ticket( val id: String, val name: String, val endTime: Date? = null ) fun Ticket.isValid(): Boolean = endTime != null
53. data class Ticket( val id: String, val name: String, val endTime: Date? = null ) val Ticket.isValid: Boolean get() = endTime != null
54. data class Ticket( val id: String, val name: String, val endTime: Date? = null ) private val Ticket.isValid: Boolean get() = endTime != null
55. data class Ticket( val id: String, val name: String, val endTime: Date? = null ) private val Ticket.isValid: Boolean get() = endTime != null
56. TicketUtils.java
57. Extension functions keep logic in scope
58. data class Ticket( val id: String, val name: String, val endTime: Date? = null ) private val Ticket.isValid: Boolean get() = endTime != null
59. data class Ticket( val id: String, val name: String, val endTime: Date? = null ) private val Ticket.isValid: Boolean get() = endTime != null ticket.
61. Part 2: A story of states
62. class TicketsScreen : Fragment()
63. class TicketsScreen : Fragment() { // initialization fun newInstance(): Fragment = //.. }
64. class TicketsScreen : Fragment() { // initialization .. // state val tickets: mutableListOf<Ticket> }
65. class TicketsScreen : Fragment() { // initialization .. // state var tickets: List<Ticket>? = null }
66. class TicketsScreen : Fragment() { // initialization .. // state lateinit var tickets: List<Ticket> }
67. class TicketsScreen : Fragment() { // initialization .. // state var tickets: List<Ticket> = emptyList() }
68. class TicketsScreen : Fragment() { // initialization .. // state var tickets: List<Ticket> = emptyList() var sortedAscending: Boolean = true }
69. class TicketsScreen : Fragment() { // initialization .. // state var tickets: List<Ticket> = emptyList() var sortedAscending: Boolean = true fun updateTickets() = //.. }
70. class TicketsScreen : Fragment() { // initialization .. // state var tickets: List<Ticket> = emptyList() var sortedAscending: Boolean = true set(value) { field = value updateTickets() } fun updateTickets() = //.. }
71. class TicketsScreen : Fragment() { // initialization .. // state .. // dependency injection @Inject lateinit var ticketService: TicketService }
72. class TicketsScreen : Fragment() { // initialization .. // state .. // dependency injection .. // view inflation .. fun onCreateView(/**/): View? = // .. }
73. class TicketsScreen : Fragment() { // initialization .. // state .. // dependency injection .. // view inflation .. // view binding .. fun onViewCreated(view: View) = // .. }
74. class TicketsScreen : Fragment() { // initialization .. // state .. // dependency injection .. // view inflation .. // view binding .. // lifecycle .. override fun onPause() = //.. }
75. class TicketsScreen : Fragment() { // initialization .. // state .. // dependency injection .. // view inflation .. // view binding .. // lifecycle .. // .. }
76. what is actually important?
77. data class ViewState( private val tickets: List<Ticket>, private val sort: Sort = descending )
78. data class ViewState( private val tickets: List<Ticket>, private val sort: Sort = descending ) enum class Sort { ascending, descending; }
79. data class ViewState( private val tickets: List<Ticket>, private val sort: Sort = descending ) enum class Sort { ascending, descending; }
80. what can happen?
81. sealed class Event { class Reloaded(val tickets: List<Ticket>) : Event() class TappedTicket(val ticket: Ticket) : Event() object TappedToggleSort : Event() }
82. sealed class Event { class Reloaded(val tickets: List<Ticket>) : Event() class TappedTicket(val ticket: Ticket) : Event() object TappedToggleSort : Event() } val event: Event when (event) { is Reloaded -> // .. is TappedTicket -> // .. TappedToggleSort -> // .. }
83. class Event { class Reloaded(val tickets: List<Ticket>) : Event() class TappedTicket(val ticket: Ticket) : Event() object TappedToggleSort : Event() } val event: Event when (event) { is Reloaded -> // .. is TappedTicket -> // .. TappedToggleSort -> // .. // ← error! }
84. class Event { class Reloaded(val tickets: List<Ticket>) : Event() class TappedTicket(val ticket: Ticket) : Event() object TappedToggleSort : Event() } val event: Event when (event) { is Reloaded -> // .. is TappedTicket -> // .. TappedToggleSort -> // .. else -> throw IllegalStateException("Hm..?") }
85. sealed class Event { class Reloaded(val tickets: List<Ticket>) : Event() class TappedTicket(val ticket: Ticket) : Event() object TappedToggleSort : Event() } val event: Event when (event) { is Reloaded -> // .. is TappedTicket -> // .. TappedToggleSort -> // .. // ← all good! }
86. Sealed class hierarchies express possible states
87. Sealed class hierarchies prevent nonsensical states
88. sealed class Event { class Reloaded(val tickets: List<Ticket>) : Event() class TappedTicket(val ticket: Ticket) : Event() object TappedToggleSort : Event() }
89. sealed class Event { class Reloaded(val tickets: List<Ticket>) : Event() class TappedTicket(val ticket: Ticket) : Event() object TappedToggleSort : Event() } sealed class Effect { data class ShowTicket(val ticket: Ticket) : Effect() }
90. sealed class Event { class Reloaded(val tickets: List<Ticket>) : Event() class TappedTicket(val ticket: Ticket) : Event() object TappedToggleSort : Event() } sealed class Effect { data class ShowTicket(val ticket: Ticket) : Effect() }
91. data class ViewState( private val tickets: List<Ticket>, private val sort: Sort = descending ) sealed class Effect { data class ShowTicket(val ticket: Ticket) : Effect() }
92. data class ViewState( private val tickets: List<Ticket>, private val sort: Sort = descending, private val effect: Effect? = null ) sealed class Effect { data class ShowTicket(val ticket: Ticket) : Effect() }
93. data class ViewState( private val tickets: List<Ticket>, private val sort: Sort = descending, private val effect: Effect? = null ) sealed class Effect { data class ShowTicket(val ticket: Ticket) : Effect() }
94. data class ViewState( private val tickets: List<Ticket>, private val sort: Sort = descending, private val effect: Effect? = null )
95. data class ViewState( private val tickets: List<Ticket>, private val sort: Sort = descending, private val effect: Effect? = null ) { fun reduce(event: Event): State { return when (event) { is Reloaded -> copy(tickets = event.tickets) is TappedTicket -> copy(effect = ShowTicket(event.ticket)) TappedToggleSort -> copy(sort = if (sort == ascending) descending else ascending) } } // ...
96. data class ViewState( private val tickets: List<Ticket>, private val sort: Sort = descending, private val effect: Effect? = null ) { // ... // UI val sortedTickets get() = if (sort == ascending) tickets.sortedBy { it.endTime } else tickets.sortedByDescending { it.endTime } // ... }
97. data class ViewState( private val tickets: List<Ticket>, private val sort: Sort = descending, private val effect: Effect? = null ) { // ... // Flow val showTicket get() = (effect as? Effect.ShowTicket)?.ticket }
98. val state = ViewState(tickets = emptyList())
99. val state = ViewState(tickets = emptyList()) val tickets = ticketService.get() val newState1 = state.reduce(Event.Reloaded(tickets))
100. val state = ViewState(tickets = emptyList()) val tickets = ticketService.get() val newState1 = state.reduce(Event.Reloaded(tickets)) val newState2 = newState1.reduce(Event.TappedToggleSort) // ...
101. Functional constructs encourage better code
102. Part 3: A story of architecture
103. object UserStore { var user: User? = null } navToProfileScreen(UserStore)
104. object UserStore { var user: User? = null } navToProfileScreen(UserStore) class UserProfileScreen(val store: UserStore) { fun bindView() { val user = store.user title.text = user.name } }
105. object UserStore { var user: User? = null } navToProfileScreen(UserStore) class UserProfileScreen(val store: UserStore) { fun bindView() { val user = store.user title.text = user.name // ← error! } }
106. object UserStore { var user: User? = null } navToProfileScreen(UserStore) class UserProfileScreen(val store: UserStore) { fun bindView() { val user = store.user title.text = user?.name ?: "Something?" } }
107. object UserStore { var user: User? = null } navToProfileScreen(UserStore) class UserProfileScreen(val store: UserStore) { fun bindView() { val user = store.user ?: throw IllegalStateException("How?") title.text = user.name } }
108. object UserStore { var user: User? = null } navToProfileScreen(UserStore) class UserProfileScreen(val store: UserStore) { fun bindView() { val user = store.user ?: throw IllegalStateException("How?") title.text = user.name } }
109. object UserStore { var user: User? = null } navToProfileScreen(UserStore) class UserProfileScreen(val store: UserStore) { fun bindView() { val user = store.user ?: throw IllegalStateException("How?") title.text = user.name } }
110. object UserStore { var user: User? = null } UserStore.user?.let { navToProfileScreen(it) } ?: navToLoginScreen() class UserProfileScreen(val store: UserStore) { fun bindView() { val user = store.user ?: throw IllegalStateException("How?") title.text = user.name } }
111. object UserStore { var user: User? = null } UserStore.user?.let { navToProfileScreen(it) } ?: navToLoginScreen() class UserProfileScreen(val user: User) { fun bindView() { title.text = user.name } }
112. object UserStore { var user: User? = null } UserStore.user?.let { navToProfileScreen(it) } ?: navToLoginScreen() class UserProfileScreen(val user: User) { fun bindView() { title.text = user.name } }
113. val user: User
114. val user: User?
115. val user: User // vs val user: User?
116. val user: User // we’re in control // vs val user: User? // ¯\_(ツ)_/¯
117. Explicit nullability forces design
118. object UserStore { var user: User? = null } class UserProfileScreen(val store: UserStore) { fun bindView() { val user = store.user ?: throw IllegalStateException("How?") title.text = user.name } }
119. object UserStore { var user: User? = null } class UserProfileScreen(val store: UserStore) { fun bindView() { val user = store.user ?: throw IllegalStateException("How?") title.text = user.name } fun logOut() { store.user = null } }
120. object UserStore { var user: User? = null } class UserProfileScreen(val store: UserStore) { fun bindView() { val user = store.user ?: throw IllegalStateException("How?") title.text = user.name } fun logOut() { store.user = null clearUserDataCache() } }
121. object UserStore { var user: User? = null } class UserProfileScreen(val store: UserStore) { fun bindView() { val user = store.user ?: throw IllegalStateException("How?") title.text = user.name } fun logOut() { store.user = null clearUserDataCache() // then send a notification, oh and take out the trash }
122. object UserStore { var user: User? = null } class UserProfileScreen(val user: User) { fun bindView() { title.text = user.name } }
123. object UserStore { var user: User? = null } class UserProfileScreen(val user: User) { fun bindView() { title.text = user.name } fun logOut() { user = null } }
124. object UserStore { var user: User? = null } class UserProfileScreen(val user: User) { fun bindView() { title.text = user.name } fun logOut() { user = null // ← error! } }
125. object UserStore { var user: User? = null } class UserProfileScreen(val user: User) { fun bindView() { title.text = user.name } fun logOut() { user = null // ← error! } }
126. object UserStore { var user: User? = null } class UserProfileScreen(val user: User, val userManager: /**/) { fun bindView() { title.text = user.name } fun logOut() { user = null // ← error! } }
127. object UserStore { var user: User? = null } class UserProfileScreen(val user: User, val userManager: /**/) { fun bindView() { title.text = user.name } fun logOut() { user = null // ← error! } }
128. object UserStore { var user: User? = null } class UserProfileScreen(val user: User, val userManager: /**/) { fun bindView() { title.text = user.name } fun logOut() { userManager.logOut() } }
129. object UserStore { var user: User? = null } class UserProfileScreen(val user: User, val userManager: /**/) { fun bindView() { title.text = user.name } fun logOut() = userManager.logOut() }
130. object UserStore { var user: User? = null } class UserProfileScreen(val user: User, val userManager: /**/) { fun bindView() { title.text = user.name } fun logOut() = userManager.logOut() }
131. var user: User
132. val user: User
133. var user: User // vs val user: User
134. var user: User // open // vs val user: User // closed
135. var user: User // search for assignments // vs val user: User // search for usages
136. Explicit mutability forces design
137. Part 4: How we got here
138. New Android Era with Kotlin by Martynas Jurkus @ Vinted Story
139. Why JetBrains Needs Kotlin by Dmitry Jemerov “ First and foremost, it’s about our own productivity.” Story
140. Story
141. Kotlin adoption in trafi-android
142. 100% Java on 2017 Jan 24
143. >67% Kotlin on 2017 Dec 19
144. Story
145. ~50% reduction in lines of code Story
146. Story
147. 10 awesome Kotlin magic tricks for rockstar software architects TO THE EXTREME!
148. Pains Style
149. Android Kotlin Style Guide
151. Pains Stability
153. >80% Kotlin on 2018 May 3
154. Dreaming of cross-platform
156. >99% Kotlin on 2018 Oct 11
157. Why Kotlin?
158. Why Kotlin? @ Trafi
159. Why JetBrains Needs Kotlin by Dmitry Jemerov “ First and foremost, it’s about our own productivity.”
160. Productivity @ Trafi
161. Productivity Focus on the human experience
162. Productivity IDE refactoring
163. Productivity Nullability in the type system
164. Productivity Functional constructs
165. Productivity Stability > performance
166. Assumptions about code are not enforceable and age badly over time Observation
167. Assumptions about code are not enforceable and age badly over time Observation Code base changes
168. Assumptions about code are not enforceable and age badly over time Observation Code base changes Other people work on it
169. Assumptions about code are not enforceable and age badly over time Observation Code base changes Other people work on it Product requirements change
170. Assumptions about code are not enforceable and age badly over time Observation Code base changes Other people work on it Product requirements change Assumptions break
171. Assumptions about code are not enforceable and age badly over time Observation
172. Suggestion Expressive types and functional constructs enforce strong contracts Assumptions about code are not enforceable and age badly over time
173. Conciseness maintains focus
174. Conciseness maintains focus Extension functions keep logic in scope
175. Conciseness maintains focus Extension functions keep logic in scope Sealed class hierarchies express state
176. Conciseness maintains focus Extension functions keep logic in scope Sealed class hierarchies express state Functional constructs encourage better code
177. Conciseness maintains focus Extension functions keep logic in scope Sealed class hierarchies express state Functional constructs encourage better code Explicit mutability forces design
178. Conciseness maintains focus Extension functions keep logic in scope Sealed class hierarchies express state Functional constructs encourage better code Explicit mutability forces design Explicit nullability forces design
179. Part 5: Where to next?
180. data class Ticket( val id: String, val name: String, val endTime: Date? = null )
181. data class Ticket( val id: TicketId, val name: String, val endTime: Date? = null )
182. typealias TicketId = String data class Ticket( val id: TicketId, val name: String, val endTime: Date? = null )
183. typealias TicketId = String data class Ticket( val id: TicketId, val name: String, val endTime: Date? = null ) val ticket = Ticket(id = "oops", name = "Ticket")
184. typealias TicketId = String data class Ticket( val id: TicketId, val name: String, val endTime: Date? = null ) val ticket = Ticket(id = "oops", name = "Ticket")
185. inline class TicketId(val id: String) data class Ticket( val id: TicketId, val name: String, val endTime: Date? = null ) val ticket = Ticket(id = "oops", name = "Ticket")
186. inline class TicketId(val id: String) data class Ticket( val id: TicketId, val name: String, val endTime: Date? = null ) val ticket = Ticket(id = "oops", name = "Ticket") // ← error!
187. inline class TicketId(val id: String) data class Ticket( val id: TicketId, val name: String, val endTime: Date? = null ) val ticket = Ticket(id = TicketId("a"), name = "Ticket") // ← ok!
188. Inline classes Kotlin 1.3 (experimental)
189. GlobalScope.launch { delay(1000L) println("C# backend developers") } println("Trafi is hiring") Thread.sleep(2000L)
190. GlobalScope.launch { delay(1000L) println("C# backend developers") } println("Trafi is hiring") Thread.sleep(2000L) // Trafi is hiring // C# backend developers
191. Coroutines Kotlin 1.3 (no longer experimental!)
192. Contracts Kotlin 1.3
193. Kotlin/Native Kotlin 1.3 (beta)
194. Typeclasses Kotlin sometime?
195. Thank you