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About this talk
• What’s a DSL
• Relevant Kotlin features
• Common examples
• My own experience
• Design demo
• How to implement DSLs
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Domain Specific Languages
• Programming languages
• Specialized to solve problems in a particular domain
HTML
Gradle build language
• Often in a declarative style
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DSL ingredients in Kotlin
• Extension functions
• Extension properties
• Lambdas with receivers
• Operator overloading
Unary operators
invoke operator
• Infix functions
• @DslMarker annotation
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Common examples
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Anko https://github.com/Kotlin/anko
verticalLayout {
val name = editText()
button("Say Hello") {
onClick {
toast("Hello, ${name.text}!")
}
}
}
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html {
body {
div {
a("http://kotlinlang.org") {
target = ATarget.blank
+"Main site"
}
}
}
}
kotlinx.html https://github.com/Kotlin/kotlinx.html
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Gradle Script Kotlin
android {
buildToolsVersion("25.0.0")
compileSdkVersion(23)
defaultConfig {
minSdkVersion(15)
targetSdkVersion(23)
applicationId = "com.example.myapp"
versionCode = 1
versionName = "1.0"
}
}
https://github.com/gradle/kotlin-dsl
android {
compileSdkVersion 23
buildToolsVersion "25.0.0"
defaultConfig {
minSdkVersion 15
targetSdkVersion 23
applicationId "com.example.myapp"
versionCode 1
versionName "1.0"
}
}
Kotlin Groovy
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object Cities : Table() {
val id = integer("id").autoIncrement().primaryKey()
val name = varchar("name", 50)
}
transaction {
val munichId = Cities.insert {
it[name] = "Munich"
} get Cities.id
Cities.insert {
it[name] = "Prague"
}
}
Exposed https://github.com/JetBrains/Exposed
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My experience
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MaterialDrawerKt https://github.com/zsmb13/MaterialDrawerKt
drawer {
closeOnClick = false
sectionHeader("Standard badges") { divider = false }
primaryItem("Primary") {
badge("111")
iicon = FontAwesome.Icon.faw_heart
}
sectionHeader("Customized badges")
primaryItem("Custom 1") {
badge("111") {
color = 0xFF0099FF
colorPressed = 0xFFCC99FF
cornersDp = 0
paddingHorizontalDp = 25
}
iicon = FontAwesome.Icon.faw_heart
selectable = false
}
}
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Tests for Twitter responses
Status
MediaEntity
Array< >
URLEntity
Array< >
HashtagEntity
Array< >
UserMentionEntity
Array< >
val status: Status = mock()
whenever(status.text) doReturn mockText
whenever(status.mediaEntities) doReturn mockMediaEntities
whenever(status.urlEntities) doReturn mockUrls
whenever(status.userMentionEntities) doReturn mockUserMentionEntities
whenever(status.hashtagEntities) doReturn mockHashtagEntities
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Tests for Twitter responses
val status: Status = mock()
whenever(status.text) doReturn mockText
whenever(status.mediaEntities) doReturn mockMediaEntities
whenever(status.urlEntities) doReturn mockUrls
whenever(status.userMentionEntities) doReturn mockUserMentionEntities
whenever(status.hashtagEntities) doReturn mockHashtagEntities
Status
MediaEntity
Array< >
URLEntity
Array< >
HashtagEntity
Array< >
UserMentionEntity
Array< > val entity: UserMentionEntity = mock()
whenever(entity.start) doReturn mockStart
whenever(entity.end) doReturn mockEnd
whenever(entity.id) doReturn mockId
whenever(entity.screenName) doReturn mockScreenName
val entity: MediaEntity = mock()
whenever(entity.start) doReturn mockStart
whenever(entity.end) doReturn mockEnd
whenever(entity.url) doReturn mockUrl
val entity: URLEntity = mock()
whenever(entity.start) doReturn mockStart
whenever(entity.end) doReturn mockEnd
whenever(entity.url) doReturn mockUrl
whenever(entity.displayURL) doReturn mockDisplayUrl
whenever(entity.expandedURL) doReturn mockExpandedUrl
val entity: HashtagEntity = mock()
whenever(entity.start) doReturn mockStart
whenever(entity.end) doReturn mockEnd
whenever(entity.text) doReturn mockText
val h1 = createHashtag(1, 4, "cool")
val h2 = createHashtag(6, 12, "awesome")
val hashtags = arrayOf(h1, h2)
val status = createStatus(hashtags, mentions, ...)
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tests {
testCase("emoji and text") {
input("hello world")
expected("hello world")
}
testCase("long, complicated status") {
input("hello t.co/a t.co/b t.co/m1 t.co/c t.co/m2 ") {
url(9 to 15, "t.co/a", "a.com", "a.com")
url(19 to 25, "t.co/b", "b.com", "b.com")
media(29 to 36, "t.co/m1")
url(40 to 46, "t.co/c", "c.c.c.com", "c.c.c.com")
media(50 to 57, "t.co/m2")
}
expected("hello a.com b.com c.c.c.com ") {
url(13 to 18, "t.co/a", "a.com", "a.com")
url(26 to 31, "t.co/b", "b.com", "b.com")
url(47 to 56, "t.co/c", "c.c.c.com", "c.c.c.com")
}
}
}
Tests for Twitter responses
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Demo
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Resources
• Village DSL
https://github.com/zsmb13/VillageDSL
• Type safe builders (official documentation)
https://kotlinlang.org/docs/reference/type-safe-builders.html
• Designing a DSL in Kotlin (Nicolas Fränkel)
https://youtu.be/fD3OqrAeaWo
• Creating DSL's in idiomatic Kotlin (Hadi Hariri)
https://youtu.be/GjGQpSFieXA