1. More readable 2. (Usually) More overhead 3. We dont know which - - PowerPoint PPT Presentation

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1. More readable 2. (Usually) More overhead 3. We dont know which - - PowerPoint PPT Presentation

Apr 20, 2023 46 likes •1.99k views

1. More readable 2. (Usually) More overhead 3. We dont know which one we aspire to more A clever title Christina Lee Two Stones, One Bird A clever title Christina Lee Kill two birds with one stone Kill two birds with one

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  • 1. More readable
  • 2. (Usually) More overhead
  • 3. We don’t know which one we aspire to more
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🙄

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A clever title

Christina Lee

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A clever title

Christina Lee

Two Stones, One Bird

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“Kill two birds with one stone”

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“Kill two birds with one stone” Accomplish two objectives with a single action ==

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Accomplish two objectives with a single action GOOD! ==

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Two for one GOOD! == One for two ???? ==

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Two for one GOOD! == One for two ???? ==

🤕

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ARGUE ON THE INTERNET!

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ARGUEMENTS ON THE INTERNET! W I N

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  • 1. Meme effectively
  • 2. (Optional) Know

something about the topic

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  • 1. Meme effectively
  • 2. (Optional) Know

something about the topic

¯\_()_/¯

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  • 2. (Optional) Know

something about the topic

☝ 👍

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Nullability

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data class Pin( val id: String, val creator: User? = null, // ... )

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fun updateAvatar(pin: Pin, avatarView: AvatarView) { if (pin.creator != null) { avatarView.bindUser(pin.creator) } }b if (pin.creator != null) { avatarView.bindUser(pin.creator) }q

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fun updateAvatar(pin: Pin, avatarView: AvatarView) { if (pin.creator != null) { avatarView.bindUser(pin.creator) } }b if (pin.creator != null) { avatarView.bindUser(pin.creator) }q

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fun updateAvatar(pin: Pin, avatarView: AvatarView) { if (pin.creator != null) { avatarView.bindUser(pin.creator) } }b if (pin.creator != null) { avatarView.bindUser(pin.creator!!) }q

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fun updateAvatar(pin: Pin, avatarView: AvatarView) { val creator = pin.creator if (creator != null) { avatarView.bindUser(creator) }q }b

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fun updateAvatar(pin: Pin, avatarView: AvatarView) { pin.creator?.let { avatarView.bindUser(it) } }b

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Nullability

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???

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Style guide

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Style guide

2

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Effective Kt

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Effective Kt

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Readability Readability Readability

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Readability Performance +

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Readability Performance +

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Readability Performance

You are here

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Nullability

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fun updateAvatar(pin: Pin, avatarView: AvatarView) { val creator = pin.creator if (creator != null) { avatarView.bindUser(creator) }q }b fun updateAvatar(pin: Pin, avatarView: AvatarView) { pin.creator?.let { avatarView.bindUser(it) } }b fun updateAvatar(pin: Pin, avatarView: AvatarView) { if (pin.creator != null) { avatarView.bindUser(pin.creator!!) }q }b

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!!

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fun updateAvatar(pin: Pin, avatarView: AvatarView) { val creator = pin.creator if (creator != null) { avatarView.bindUser(creator) }a }b fun updateAvatar(pin: Pin, avatarView: AvatarView) { pin.creator?.let { avatarView.bindUser(it) }c }d

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public static final void updateAvatar(@NotNull Pin pin, @NotNull AvatarView avatarView) { Intrinsics.checkParameterIsNotNull(pin, "pin"); Intrinsics.checkParameterIsNotNull(avatarView, "avatarView"); User creator = pin.getCreator(); if(creator != null) { avatarView.bindUser(creator); }a }b fun updateAvatar(pin: Pin, avatarView: AvatarView) { val creator = pin.creator if (creator != null) { avatarView.bindUser(creator) }a }b

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public static final void updateAvatar(@NotNull Pin pin, @NotNull AvatarView avatarView) { Intrinsics.checkParameterIsNotNull(pin, "pin"); Intrinsics.checkParameterIsNotNull(avatarView, "avatarView"); User creator = pin.getCreator(); if(creator != null) { avatarView.bindUser(creator); }a }b

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fun updateAvatar(pin: Pin, avatarView: AvatarView) { val creator = pin.creator if (creator != null) { avatarView.bindUser(creator) }a }b fun updateAvatar(pin: Pin, avatarView: AvatarView) { pin.creator?.let { avatarView.bindUser(it) }c }d

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fun updateAvatar(pin: Pin, avatarView: AvatarView) { pin.creator?.let { avatarView.bindUser(it) }c }d

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public static final void updateAvatar(@NotNull Pin pin, @NotNull AvatarView avatarView) { Intrinsics.checkParameterIsNotNull(pin, "pin"); Intrinsics.checkParameterIsNotNull(avatarView, "avatarView"); User var10000 = pin.getCreator(); if(var10000 != null) { User var2 = var10000; avatarView.bindUser(var2); }e }f

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public static final void updateAvatar(@NotNull Pin pin, @NotNull AvatarView avatarView) { Intrinsics.checkParameterIsNotNull(pin, "pin"); Intrinsics.checkParameterIsNotNull(avatarView, "avatarView"); User var10000 = pin.getCreator(); if(var10000 != null) { User var2 = var10000; avatarView.bindUser(var2); } }

😲

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L1 LINENUMBER 13 L1 ALOAD 0 // load pin INVOKEVIRTUAL Pin.getCreator () //invoke getter ASTORE 2 // store in field 2 L2 LINENUMBER 14 L2 ALOAD 2 // load field 2 (user) IFNULL L3 // if user is null, jump to return L4 LINENUMBER 15 L4 ALOAD 1 // load view ALOAD 2 // load user INVOKEVIRTUAL AvatarView.bindUser() //invoke L3 LINENUMBER 22 L3 RETURN if (creator == null)

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L1 LINENUMBER 13 L1 ALOAD 0 // load pin from ref 0 INVOKEVIRTUAL Pin.getCreator() // invoke pin.getCreator() DUP // duplicate returned value IFNULL L2 // if null pop ASTORE 2 // store creator value in field 2 L3 ALOAD 2 // load ref 2 onto stack ASTORE 3 // store in field 3 L4 LINENUMBER 14 L4 ALOAD 1 // load “avatarView” ALOAD 3 // load value of pin.getCreator() INVOKEVIRTUAL AvatarView.bindUser L2 POP pin.creator?.let { }

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L1 LINENUMBER 13 L1 ALOAD 0 // load pin INVOKEVIRTUAL Pin.getCreator() // invoke getter ASTORE 2 // store result in field 2 L2 LINENUMBER 14 L2 ALOAD 2 // load creator DUP // duplicate IFNULL L3 // if null?? ASTORE 3 // store in field 3 L4 ALOAD 3 // load field 3 ASTORE 4 // store in field 4 L5 LINENUMBER 15 L5 ALOAD 1 // load view ALOAD 4 // load user INVOKEVIRTUAL AvatarView.bindUser(v) //invoke view with user val creator = pin.creator; creator?.let { }

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TL;DR: Idk

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TL;DR: It doesn’t matter*

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val creator = pin.creator if (creator != null) { avatarView.bindUser(creator) } vs. pin.creator?.let { avatarView.bindUser(it) }

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val creator = pin.creator if (creator != null) { val firstName = creator.firstName if (firstName != null) { avatarView.setFirstName(firstName) } } vs. pin.creator?.firstName?.let { avatarView.setFirstName(it) }

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val creator = pin.creator if (creator != null) { val firstName = creator.firstName if (firstName != null) { avatarView.setFirstName(firstName) } } else { } vs. pin.creator?.firstName?.let { avatarView.setFirstName(it) }.orElse { }

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val creator = pin.creator if (creator != null && creator.firstName != null) { avatarView.setFirstName(firstName) } else { } vs. pin.creator?.firstName?.let { avatarView.setFirstName(it) }.orElse { }

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Lean towards let

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Lean towards let*

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Lean towards let*

* Brought to you by Twitter

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Lean towards let

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with / apply let / also

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with / apply let / also

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with / apply let / also

public inline fun <T, R> with( receiver: T, block: T.() -> R ): R = receiver.block()

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with / apply let / also

public inline fun <T, R> with( receiver: T, block: T.() -> R ): R = receiver.block()

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with / apply let / also

public inline fun <T, R> with( receiver: T, block: T.() -> R ): R = receiver.block() with(foo) {h foo.bar() foo.baz() }g

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with / apply let / also

public inline fun <T, R> with( receiver: T, block: T.() -> R ): R = receiver.block() with(foo) {h bar() baz() }g

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with / apply let / also

public inline fun <T, R> with( receiver: T, block: T.() -> R ): R = receiver.block()

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with / apply let / also

public inline fun <T, R> with( receiver: T, block: T.() -> R ): R = receiver.block()

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with / apply let / also

foo.bar() foo.baz() foo.bam()

Same receiver multiple times Logically grouped functions

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with / apply let / also

with(db) {

  • pen()

commit(obj) close() }

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with / apply let / also

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with / apply let / also

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with / apply let / also

public inline fun <T> T.apply( block: T.() -> Unit ): T { block(); return this }a

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with / apply let / also

public inline fun <T> T.apply( block: T.() -> Unit ): T { block(); return this }a

Extension function

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with / apply let / also

public inline fun <T> T.apply( block: T.() -> Unit ): T { block(); return this }a

Lambda + Receiver

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with / apply let / also

public inline fun <T> T.apply( block: T.() -> Unit ): T { block(); return this }a

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with / apply let / also

public inline fun <T> T.apply( block: T.() -> Unit ): T { block(); return this }a

“I need this object, but I need to run a bit of code on it before I use it”

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with / apply let / also

public inline fun <T> T.apply( block: T.() -> Unit ): T { block(); return this }a

INITIALIZATIONS

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with / apply let / also

val myTextView = TextView(context).apply { layoutParams = LinearLayout.LayoutParams(...) }

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with / apply let / also

return foo.apply { baz() }

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with / apply let / also

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with / apply let / also

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with / apply let / also

public inline fun <T, R> T.let( block: (T) -> R ): R = block(this)

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with / apply let / also

public inline fun <T, R> T.let( block: (T) -> R ): R = block(this) Everything but with() Spoiler Alert:

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with / apply let / also

public inline fun <T, R> T.let( block: (T) -> R ): R = block(this)

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with / apply let / also

public inline fun <T, R> T.let( block: (T) -> R ): R = block(this)

😲

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with / apply let / also

val usernameView: View? = user.name?.let { name -> ViewWithText(context, name) }

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with / apply let / also

DexMethods.kt: http://bit.ly/2xFN3Bd

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with / apply let / also

Nullablity 🎊 🎊

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with / apply let / also

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with / apply let / also

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with / apply let / also

public inline fun <T> T.also( block: (T) -> Unit ): T { block(this); return this }a

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with / apply let / also

public inline fun <T> T.also( block: (T) -> Unit ): T { block(this); return this }a

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with / apply let / also

public inline fun <T> T.also( block: (T) -> Unit ): T { block(this); return this }a

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with / apply let / also

public inline fun <T> T.also( block: (T) -> Unit ): T { block(this); return this }a

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with / apply let / also

public inline fun <T> T.also( block: (T) -> Unit ): T { block(this); return this }a Plain lambda

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with / apply let / also

public inline fun <T> T.also( block: (T) -> Unit ): T { block(this); return this }a

“Oh and also…”

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with / apply let / also

foo.bar() .also { } .baz()

“Oh and also…”

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???

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Are you calling repeated functions on an object? Do you need to return the object? Do you need to return the object? No Yes Yes No Apply With No Yes Also Let

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need caller to be returned don’t need caller returned need receiver apply with don’t need receiver also let

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  • 1. Things return values you don’t

always need to use

  • 2. You can call non-receiver functions

inside lambdas with receivers

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val idk = with(foo) { bar() baz() }

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val idk: Baz = with(foo) { bar() baz() }

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val idk: Baz = with(foo) { bar() createBaz() }

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With: Logically grouped calls on an object Apply: Initialization or configuration Let: Nulls + conversions of single objects Also: Ancillary/Side effect-y code in chains

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With: Logically grouped calls on an object Apply: Initialization or configuration Let: Nulls + conversions of single objects Also: Ancillary/Side effect-y code in chains Run: ???

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run

public inline fun <R> run( block: () -> R ): R = block() public inline fun <T, R> T.run( block: T.() -> R ): R = block()

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run

public inline fun <R> run( block: () -> R ): R = block()

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run

public inline fun <R> run( block: () -> R ): R = block() No arg block

  • f code

Return value

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run

public inline fun <R> run( block: () -> R ): R = block() fun myFun(user: User) { val foo = Foo() run { foo.baz() foo.bar() } }

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run

public inline fun <R> run( block: () -> R ): R = block() fun myFun(user: User) { val foo = Foo() { foo.baz() foo.bar() }() }

🤕

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run

public inline fun <R> run( block: () -> R ): R = block() fun myFun(user: User) { val foo = Foo() { foo.baz() foo.bar() }() }

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run

public inline fun <R> run( block: () -> R ): R = block() fun myFun(user: User) { val foo = Foo() foo.baz() foo.bar() }

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fun myFun(user: User) { val foo = Foo() val result = run { foo.baz() foo.bar() } }

run

public inline fun <R> run( block: () -> R ): R = block()

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fun myFun(user: User) { val foo = Foo() val result = { foo.baz() foo.bar() }() }

run

public inline fun <R> run( block: () -> R ): R = block()

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val repo = currentRepo ?: run { initializeRepo() }

run

public inline fun <R> run( block: () -> R ): R = block()

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run

public inline fun <R> run( block: () -> R ): R = block() public inline fun <T, R> T.run( block: T.() -> R ): R = block()

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run

public inline fun <T, R> T.run( block: T.() -> R ): R = block()

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run

public inline fun <T, R> T.run( block: T.() -> R ): R = block() public inline fun <T, R> with( receiver: T, block: T.() -> R ): R = receiver.block()

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run

with(db) {

  • pen()

commit() close() } vs. db?.run {

  • pen()

commit() close() } Can insert ?. Don’t want return value

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run

with(db) {

  • pen()

commit() close() } vs. db?.run {

  • pen()

commit() close() } Can insert ?. Don’t want return value if (db != null) { //lambda with receiver }

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run

with(db) {

  • pen()

commit() close() } vs. db.run {

  • pen()

commit() close() } Can insert ?. Don’t want return value

¯\_()_/¯

if (db != null) { //lambda with receiver }

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With: Logically grouped calls on an object Apply: Initialization or configuration Let: Nulls + conversions of single objects Also: Ancillary/Side effect-y code in chains Run: With + nullability (?: and ?.)

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With: Logically grouped calls on an object Apply: Initialization or configuration Let: Nulls (and maybe conversions of single objects) Also: Ancillary/Side effect-y code in chains Run: With + nullability (?: and ?.)

(Maybe…?)

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Array<Int>

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Array<Int> IntArray

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Array<Int> IntArray ¯\_()_/¯

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Non null types in Kotlin tend to be compiled to Java’s primitives

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List<Int> (Kotlin) List<Integer> (Java)

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Array<Int> (Kotlin) Integer[]

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Array<Int> (Kotlin) Integer[] Object[] result$iv = new Integer[size$iv];

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Array<Int> (Kotlin) Integer[] int[] ?

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Array<Int> (Kotlin) Integer[] int[] IntArray

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Array<Int> (Kotlin) Integer[] int[] IntArray int[] result$iv = new int[size$iv];

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Array<Int> Integer[] int[] IntArray

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Array<Int> Integer[] int[] IntArray

Performance

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Array<Int> Integer[] int[] IntArray

Performance

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Array<Int> Integer[] int[] IntArray

Performance

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Delegates.notNull vs lateinit

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Lateinit Delegates.notNull

must be a variable -> can be reassigned can’t be a “primitive” can be a “primitive” can be val or var

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Lateinit Delegates.notNull

must be a variable -> can be reassigned can’t be a “primitive” can be a “primitive” can be val or var

Basically no restrictions

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Lateinit Delegates.notNull

must be a variable -> can be reassigned can’t be a “primitive” can be a “primitive” can be val or var

Forcing functions: val(?) or primitive

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Delegates.notNull

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Delegates.notNull

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Delegates.notNull

private class NotNullVar<T: Any>() : ReadWriteProperty<Any?, T> { private var value: T? = null public override fun getValue(...): T { return value ?: throw IllegalStateException( "Property ${property.name} should be initialized before get.") } public override fun setValue(..., value: T) { this.value = value } }

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private class NotNullVar<T: Any>() : ReadWriteProperty<Any?, T> { private var value: T? = null public override fun getValue(...): T { return value ?: throw IllegalStateException( "Property ${property.name} should be initialized before get.") } public override fun setValue(..., value: T) { this.value = value } }

Delegates.notNull

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private class NotNullVar<T: Any>() : ReadWriteProperty<Any?, T> { private var value: T? = null public override fun getValue(...): T { return value ?: throw IllegalStateException( “Property ${property.name} should be initialized before get.") } public override fun setValue(..., value: T) { this.value = value } }

Delegates.notNull

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private class NotNullVar<T: Any>() : ReadWriteProperty<Any?, T> { private var value: T? = null public override fun getValue(...): T { return value ?: throw IllegalStateException( Property ${property.name} should be initialized before get.") } public override fun setValue(..., value: T) { this.value = value } }

Delegates.notNull

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Delegates.notNull

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Delegates.notNull?

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lateinit

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late initialized

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late initialized

class User { val firstName: String = "Christina" val lastName: String init { lastName = "Lee" } }

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late initialized

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late initialized

class TestActivity : AppCompatActivity() { lateinit var button: Button

  • verride fun onCreate(savedInstanceState: Bundle?) {

super.onCreate(savedInstanceState) setContentView(R.layout.activity_test) button = findViewById(R.id.button) as Button } }

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???

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late initialized:

when you can

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late initialized:

when you can*

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Inline fun vs Custom getter

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class User(val firstName: String, val lastName: String, var height: Inch) { val isTall get() = height > SixFeet }a

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class User(val firstName: String, val lastName: String, var height: Inch) { fun isTall(): Boolean = height > SixFeet }a

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val me = User(firstName = "Christina", lastName = "Lee", height = 68)

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val me = User(firstName = "Christina", lastName = "Lee", height = 68) vs me.isTall me.isTall()

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val me = User(firstName = "Christina", lastName = "Lee", height = 68) me.isTall me.isTall()

?

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me.isTall me.isTall()

?

public final isTall2()Z L0 LINENUMBER 18 L0 ALOAD 0 GETFIELD User.height : I BIPUSH 72 IF_ICMPLE L1 ICONST_1 GOTO L2 L1 ICONST_0 L2 IRETURN L3 LOCALVARIABLE this User; L0 L3 0 MAXSTACK = 2 MAXLOCALS = 1 public final isTall1()Z L0 LINENUMBER 16 L0 ALOAD 0 GETFIELD User.height : I BIPUSH 72 IF_ICMPLE L1 ICONST_1 GOTO L2 L1 ICONST_0 L2 IRETURN L3 LOCALVARIABLE this User; L0 L3 0 MAXSTACK = 2 MAXLOCALS = 1
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me.isTall me.isTall()

?

public final isTall2()Z L0 LINENUMBER 18 L0 ALOAD 0 GETFIELD User.height : I BIPUSH 72 IF_ICMPLE L1 ICONST_1 GOTO L2 L1 ICONST_0 L2 IRETURN L3 LOCALVARIABLE this User; L0 L3 0 MAXSTACK = 2 MAXLOCALS = 1 public final isTall1()Z L0 LINENUMBER 16 L0 ALOAD 0 GETFIELD User.height : I BIPUSH 72 IF_ICMPLE L1 ICONST_1 GOTO L2 L1 ICONST_0 L2 IRETURN L3 LOCALVARIABLE this User; L0 L3 0 MAXSTACK = 2 MAXLOCALS = 1
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me.isTall me.isTall()

?

public final isTall2()Z L0 LINENUMBER 18 L0 ALOAD 0 GETFIELD User.height : I BIPUSH 72 IF_ICMPLE L1 ICONST_1 GOTO L2 L1 ICONST_0 L2 IRETURN L3 LOCALVARIABLE this User; L0 L3 0 MAXSTACK = 2 MAXLOCALS = 1

There is no difference in implementation or performance; they only differ in readability.

  • Kotlin in Action, pg 26
public final isTall1()Z L0 LINENUMBER 16 L0 ALOAD 0 GETFIELD User.height : I BIPUSH 72 IF_ICMPLE L1 ICONST_1 GOTO L2 L1 ICONST_0 L2 IRETURN L3 LOCALVARIABLE this User; L0 L3 0 MAXSTACK = 2 MAXLOCALS = 1
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me.isTall me.isTall()

?

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me.isTall me.isTall()

?

me.firstName me.lastName me.age

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me.isTall me.isTall()

?

me.firstName me.lastName me.age me.getFriends() me.clear() me.clone()

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me.isTall me.isTall()

?

me.firstName me.lastName me.age me.getFriends() me.clear() me.clone()

data

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me.isTall me.isTall()

?

me.firstName me.lastName me.age me.getFriends() me.clear() me.clone()

data actions

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me.isTall me.isTall()

?

data actions attribute of the type

  • n the order of a field access

no overt side effects computationally expensive conversions or copies return value changes each time

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me.isTall me.isTall()

?

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SLIDE 171

me.isTall me.isTall()

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SLIDE 172

Map/Filter + Sequence

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SLIDE 173 * Elements in the set returned are sorted according to the given [comparator]. */ @kotlin.jvm.JvmVersion public fun <T> Array<out T>.toSortedSet(comparator: Comparator<in T>): SortedSet<T> { return toCollection(TreeSet<T>(comparator)) } /** * Returns a single list of all elements yielded from results of [transform] function being invoked on each element of original array. */ public inline fun <T, R> Array<out T>.flatMap(transform: (T) -> Iterable<R>): List<R> { return flatMapTo(ArrayList<R>(), transform) } /** * Appends all elements yielded from results of [transform] function being invoked on each element of original array, to the given [destination]. */ public inline fun <T, R, C : MutableCollection<in R>> Array<out T>.flatMapTo(destination: C, transform: (T) -> Iterable<R>): C { for (element in this) { val list = transform(element) destination.addAll(list) } return destination } /** * Groups elements of the original array by the key returned by the given [keySelector] function * applied to each element and returns a map where each group key is associated with a list of corresponding elements. * * The returned map preserves the entry iteration order of the keys produced from the original array. * * @sample samples.collections.Collections.Transformations.groupBy */ public inline fun <T, K> Array<out T>.groupBy(keySelector: (T) -> K): Map<K, List<T>> { return groupByTo(LinkedHashMap<K, MutableList<T>>(), keySelector) } /** * Groups values returned by the [valueTransform] function applied to each element of the original array * by the key returned by the given [keySelector] function applied to the element * and puts to the [destination] map each group key associated with a list of corresponding values. * * @return The [destination] map. * * @sample samples.collections.Collections.Transformations.groupByKeysAndValues */ public inline fun <T, K, V, M : MutableMap<in K, MutableList<V>>> Array<out T>.groupByTo(destination: M, keySelector: (T) -> K, valueTransform: (T) -> V): M { for (element in this) { val key = keySelector(element) val list = destination.getOrPut(key) { ArrayList<V>() } list.add(valueTransform(element)) }
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val arr = arrayOf("1", "2", "3", “4”) val numGreaterThanTwo = arr.map { Integer.valueOf(it) } .filter { it > 2 } .count()

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SLIDE 175 Object[] elements$iv = new String[]{"1", "2", "3", “4"}; Object[] $receiver$iv = (Object[])elements$iv; Object[] $receiver$iv$iv = $receiver$iv; Collection destination$iv$iv = (Collection)(new ArrayList($receiver$iv.length)); Object element$iv$iv; for(int var6 = 0; var6 < $receiver$iv$iv.length; ++var6) { element$iv$iv = $receiver$iv$iv[var6]; String it = (String)element$iv$iv; Integer var13 = Integer.valueOf(it); destination$iv$iv.add(var13); }a Iterable $receiver$iv = (Iterable)((List)destination$iv$iv); destination$iv$iv = (Collection)(new ArrayList()); Iterator var17 = $receiver$iv.iterator(); while(var17.hasNext()) { element$iv$iv = var17.next(); Integer it = (Integer)element$iv$iv; if(Intrinsics.compare(it.intValue(), 2) > 0) { destination$iv$iv.add(element$iv$iv); }b }c Collection var16 = (Collection)((List)destination$iv$iv); int numbersGreaterThanTwo = var16.size();
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SLIDE 176 Object[] elements$iv = new String[]{"1", "2", "3", “4"}; Object[] $receiver$iv = (Object[])elements$iv; Object[] $receiver$iv$iv = $receiver$iv; Collection destination$iv$iv = (Collection)(new ArrayList($receiver$iv.length)); Object element$iv$iv; for(int var6 = 0; var6 < $receiver$iv$iv.length; ++var6) { element$iv$iv = $receiver$iv$iv[var6]; String it = (String)element$iv$iv; Integer var13 = Integer.valueOf(it); destination$iv$iv.add(var13); }a Iterable $receiver$iv = (Iterable)((List)destination$iv$iv); destination$iv$iv = (Collection)(new ArrayList()); Iterator var17 = $receiver$iv.iterator(); while(var17.hasNext()) { element$iv$iv = var17.next(); Integer it = (Integer)element$iv$iv; if(Intrinsics.compare(it.intValue(), 2) > 0) { destination$iv$iv.add(element$iv$iv); }b }c Collection var16 = (Collection)((List)destination$iv$iv); int numbersGreaterThanTwo = var16.size();
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SLIDE 177 Object[] elements$iv = new String[]{“1", "2", "3", “4"}; Collection destination$iv$iv = (Collection)(new ArrayList($receiver$iv.length)); Object element$iv$iv; for(int var6 = 0; var6 < $receiver$iv$iv.length; ++var6) { Integer var13 = Integer.valueOf(it); }a destination$iv$iv = (Collection)(new ArrayList()); while(var17.hasNext()) { if(Intrinsics.compare(it.intValue(), 2) > 0) { destination$iv$iv.add(element$iv$iv); }b }c int numbersGreaterThanTwo = var16.size();
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SLIDE 178 Collection destination$iv$iv = (Collection)(new ArrayList($receiver$iv.length)); Object element$iv$iv; for(int var6 = 0; var6 < $receiver$iv$iv.length; ++var6) { Integer var13 = Integer.valueOf(it); } destination$iv$iv = (Collection)(new ArrayList()); while(var17.hasNext()) { if(Intrinsics.compare(it.intValue(), 2) > 0) { destination$iv$iv.add(element$iv$iv); } }
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SLIDE 179 Collection destination$iv$iv = (Collection)(new ArrayList($receiver$iv.length)); Object element$iv$iv; for(int var6 = 0; var6 < $receiver$iv$iv.length; ++var6) { Integer var13 = Integer.valueOf(it); } destination$iv$iv = (Collection)(new ArrayList()); while(var17.hasNext()) { if(Intrinsics.compare(it.intValue(), 2) > 0) { destination$iv$iv.add(element$iv$iv); } }

Intermediate Collections

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SLIDE 180 Collection destination$iv$iv = (Collection)(new ArrayList($receiver$iv.length)); Object element$iv$iv; for(int var6 = 0; var6 < $receiver$iv$iv.length; ++var6) { Integer var13 = Integer.valueOf(it); } destination$iv$iv = (Collection)(new ArrayList()); while(var17.hasNext()) { if(Intrinsics.compare(it.intValue(), 2) > 0) { destination$iv$iv.add(element$iv$iv); } }

Intermediate Collections

large collections

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val arr = arrayOf(“1", "2", "3", “4") val numGreaterThanTwo = arr.asSequence() .map { Integer.valueOf(it) } .filter { it > 2 } .count()

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SLIDE 182

arr.asSequence() .map { } .filter { } .count() arr.map { } .filter { } .count() Mapping 1 Filtering 1 Mapping 2 Filtering 2 Mapping 3 Filtering 3 Mapping 4 Filtering 4 Mapping 1 Mapping 2 Mapping 3 Mapping 4 Filtering 1 Filtering 2 Filtering 3 Filtering 4

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SLIDE 183

arr.asSequence() .map { } .filter { } arr.map { } .filter { } Mapping 1 Mapping 2 Mapping 3 Mapping 4 Filtering 1 Filtering 2 Filtering 3 Filtering 4

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SLIDE 184

arr.asSequence() .map { } .filter { } arr.map { } .filter { } Mapping 1 Mapping 2 Mapping 3 Mapping 4 Filtering 1 Filtering 2 Filtering 3 Filtering 4

Requires a terminal operation

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internal class TransformingSequence<T, R> constructor(private val sequence: Sequence<T>, private val transformer: (T) -> R) : Sequence<R> {

  • verride fun iterator(): Iterator<R> = object : Iterator<R> {

val iterator = sequence.iterator()

  • verride fun next(): R {

return transformer(iterator.next()) }b

  • verride fun hasNext(): Boolean {

return iterator.hasNext() } } // . . . }

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SLIDE 186
  • verride fun next(): R {

return transformer(iterator.next()) }b

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for (item in this) destination.add(transform(item)) return destination

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Performance

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Wholistic Performance

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Performance

Intermediate Collections Object allocations + Capturing references

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Use asSequence if you have a compelling large data set

  • r have profiled perf issues.

Rule of thumb:

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The End

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Christina Lee

@RunChristinaRun

👌