DSL Design (Kotlin Budapest User Group meetup - September)

A talk presenting the basics of what a DSL is, what use cases there are for them, and looking at some of the design choices we can make while creating one.

Transcript

1. DSL design
   Márton Szabolcs Braun
   zsmb13
   zsmb13@sch.bme.hu zsmb13
   

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2. 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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3. 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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4. 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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5. Common examples
   

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6. Anko https://github.com/Kotlin/anko
   verticalLayout {
   val name = editText()
   button("Say Hello") {
   onClick {
   toast("Hello, ${name.text}!")
   }
   }
   }
   

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7. html {
   body {
   div {
   a("http://kotlinlang.org") {
   target = ATarget.blank
   +"Main site"
   }
   }
   }
   }
   kotlinx.html https://github.com/Kotlin/kotlinx.html
   

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8. 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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9. 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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10. My experience
    

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11. 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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12. 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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13. 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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14. 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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15. Demo
    

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16. 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
    

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17. Photo:
    Alexey Sergeev
    DSL design
    zsmb13
    zsmb13@sch.bme.hu zsmb13
    

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