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Meta-Programming with Kotlin
@_jitinsharma
Jitin Sharma
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Open Ended
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Open Ended
Automation
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Open Ended
Automation
Kotlin
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Meta-Programming
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Code Generators Code Parsers
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Code Generators Code Parsers
Annotation Processors?
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Code Generators Code Parsers
Annotation Processors?
Retrofit
Gson
Dagger
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Source Code Parsers
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Source Code Parsers?
• Gain insights over large codebase
• Build static analysis tools
• Documentation!
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Anatomy of Source Code
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File
Class
class… Functions Variables
• abstract
• interface
• static
• ….
• private
• protected
• public
• ….
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File
Classes
Functions Variables
class… Functions Variables
• abstract
• interface
• object
• companion
• data
• ….
• private
• internal
• typealias
• ….
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val source: String = System.getProperty("user.dir")
class Generator : GeneratorConfig {
private var replaceIfNecessary = false
override fun createConfig(config: Config) {
}
inner class Template {
...
}
data class Model(...)
}
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Program
Structure
Interface
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PSI
• Provides hierarchal content of code
• Works across languages
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PSI
PsiFileFactory
.getInstance(project)
.createFileFromText(KotlinLanguage.INSTANCE, text)
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PSI
PsiFileFactory
.getInstance(project)
.createFileFromText(KotlinLanguage.INSTANCE, text)
private val project by lazy {
KotlinCoreEnvironment.createForProduction(
Disposer.newDisposable(),
CompilerConfiguration(),
EnvironmentConfigFiles.JVM_CONFIG_FILES
).project
}
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implementation("org.jetbrains.kotlin:kotlin-compiler-embeddable:1.3.61")
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PsiFile
PsiElement PsiElement
PsiElement …
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PsiFile
PsiElement PsiElement
PsiElement …
KtFile
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ArrowView.kt
import android.content.Context
import android.graphics.Canvas
import android.graphics.Color
class ArrowView(context: Context, sides: Float, val base: Float)
: View(context) {
private fun createIconView(drawable: Drawable): ImageView {
val imageView = AppCompatImageView(context)
imageView.scaleType = ImageView.ScaleType.CENTER
...
return imageView
}
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ArrowView.kt
import android.content.Context
import android.graphics.Canvas
import android.graphics.Color
class ArrowView(context: Context, sides: Float, val base: Float)
: View(context) {
private fun createIconView(drawable: Drawable): ImageView {
val imageView = AppCompatImageView(context)
imageView.scaleType = ImageView.ScaleType.CENTER
...
return imageView
}
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ArrowView.kt
KtFile
}
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ArrowView.kt
import android.content.Context
import android.graphics.Canvas
import android.graphics.Color
class ArrowView(context: Context, sides: Float, val base: Float)
: View(context) {
private fun createIconView(drawable: Drawable): ImageView {
val imageView = AppCompatImageView(context)
imageView.scaleType = ImageView.ScaleType.CENTER
...
return imageView
}
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import android.content.Context
import android.graphics.Canvas
import android.graphics.Color
KtImportList
KtImportDirective
}
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import android.content.Context
import android.graphics.Canvas
import android.graphics.Color
KtImportList
KtImportAlias
as AndroidColor
KtImportDirective
}
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ArrowView.kt
import android.content.Context
import android.graphics.Canvas
import android.graphics.Color
class ArrowView(context: Context, sides: Float, val base: Float)
: View(context) {
private fun createIconView(drawable: Drawable): ImageView {
val imageView = AppCompatImageView(context)
imageView.scaleType = ImageView.ScaleType.CENTER
...
return imageView
}
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class ArrowView(context: Context, sides: Float, val base: Float)
: View(context) {
KtClass
KtSuperTypeEntries
}
}
KtPrimaryConstructor
}
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ArrowView.kt
import android.content.Context
import android.graphics.Canvas
import android.graphics.Color
class ArrowView(context: Context, sides: Float, val base: Float)
: View(context) {
private fun createIconView(drawable: Drawable): ImageView {
val imageView = AppCompatImageView(context)
imageView.scaleType = ImageView.ScaleType.CENTER
...
return imageView
}
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private fun createIconView(drawable: Drawable): ImageView {
val imageView = AppCompatImageView(context)
imageView.scaleType = ImageView.ScaleType.CENTER
...
return imageView
}
KtParameter
KtModifierKeywordToken KtTypeReference
KtBlockExpression
}
}
}
}
KtExpression
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private fun createIconView(drawable: Drawable): ImageView {
val imageView = AppCompatImageView(context)
imageView.scaleType = ImageView.ScaleType.CENTER
...
return imageView
}
/**
* Generates an imageview dynamically
*/
KDoc
}
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ArrowView.kt
import android.content.Context
import android.graphics.Canvas
import android.graphics.Color
class ArrowView(context: Context, sides: Float, val base: Float)
: View(context) {
private fun createIconView(drawable: Drawable): ImageView {
val imageView = AppCompatImageView(context)
imageView.scaleType = ImageView.ScaleType.CENTER
...
return imageView
}
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PSI-Tree
ktFile.acceptChildren(// PsiElementVisitor())
ktFile.acceptChildren(classRecursiveVisitor { ktClass ->
})
ktFile.acceptChildren(namedFunctionRecursiveVisitor { ktFunction ->
})
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No content
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Plugin
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Source Code as Data
Source
Code
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Source Code as Data
Source
Code
@Serializable
data class ParsedFile(
var name: String,
var doc: String? = null,
@SerialName("classes")
var parsedClasses: List? = null,
@SerialName("functions")
var parsedFunctions: List? = null,
@SerialName("properties")
var parsedVariables: List? = null
)
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Source Code as Data
Source
Code
@Serializable
data class ParsedFile(
var name: String,
var doc: String? = null,
@SerialName("classes")
var parsedClasses: List? = null,
@SerialName("functions")
var parsedFunctions: List? = null,
@SerialName("properties")
var parsedVariables: List? = null
)
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Documentation
• dokka != configurable
• Build custom documentation
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Static Analysis
• Access to every piece of code in your codebase
• ktlint!
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Source Code Generators
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Source Code Generators?
• Avoid manual boilerplate code
• Promote templating
• Create more formalised code base
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Writing Source Code
• Easy string manipulation with regex and
indent extensions
• Java8 provides better file operations and
Streams!
• Coroutines for async
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Writing Templates
val text =
"""
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
}
}
""".trimIndent()
Files.write(path, text)
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Writing Templates
val text =
"""
class $activityName : BaseActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.$layoutName)
}
}
""".trimIndent()
Files.write(path, text)
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Structured Codegen
https://github.com/square/kotlinpoet
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Structured Codegen
FileSpec.builder("in.jitinsharma", "MainActivity.kt")
TypeSpec.classBuilder()
FunSpec.builder("onCreate")
addParameter()
addModifiers(KModifier.INTERNAL)
superclass(TypeVariableName.invoke("AppCompatActivity"))
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Schema based Codegen
{
"source": "...",
“type": "...",
"paths": []
}
Source
Code
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Schema based Codegen
{
"sourceClass": "MainActivity.kt",
"sourceXml": "activity_main",
"adapter": "CountryListAdapter",
"views": [
{
"layoutFileName": "country_list_header.xml",
"layoutType": "TextView",
"viewHolderName": "CountryListHeaderViewHolder"
}
]
}
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SqlDelight
CREATE TABLE Photos (
id INTEGER NOT NULL,
title TEXT NOT NULL
);
insert:
INSERT INTO Photos (id, title) VALUES (?, ?);
getAll:
SELECT * FROM Photos;
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SqlDelight
interface PhotoQueries : Transacter {
fun getAll(mapper: (
id: String,
title: String
) -> T): Query
fun getAll(): Query
fun insert(
id: String,
title: String
)
}
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val db = Database(AndroidSqliteDriver(Database.Schema, context, “photo.db”))
db.photoQueries.getAll() -> List
SqlDelight - MPP
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No content
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T.use()
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T.use()
codeString
.lineSequence()
.map { line -> }
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T.use()
codeString
.lineSequence()
.map { line -> }
Files.find(path, 10,
BiPredicate { path, _ -> })
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T.use()
codeString
.lineSequence()
.map { line -> }
Files.find(path, 10,
BiPredicate { path, _ -> })
Files.write(
path,
classString.toByteArray(),
StandardOpenOption.CREATE_NEW,
StandardOpenOption.TRUNCATE_EXISTING)
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.
├── app
├── module-1
├── module-2
├── …
└── tools-module
java -jar project/build/libs/tools.jar --param
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.
├── app
├── module-1
├── module-2
├── …
└── script.kts
kscript
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Fun fact
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Thanks
@_jitinsharma