Summary - Compiler plugins
- Kotlin course
- Expert
- Lesson 18/47
- 5 min
Combine IR, all-open and no-arg to write a framework integration.
Summary - Compiler plugin
In this group you learned compiler plugin, IR, plugin vs KSP, all-open and no-arg. Now you will write a model that combines them: an open Entity and its subclass.
Your Entity will be open; its tag() method will also be open. A User subclass will override tag(). In main you will do a polymorphic assignment and print the result. This is a typical entity scenario where all-open and no-arg meet.
Combining: open Entity
Now we will do by hand what all-open does: mark Entity and tag() as open. Then add a subclass.
Example: open class Entity(val id: Int) { open fun tag(): String = "Entity" }. class User(id: Int) : Entity(id) { override fun tag(): String = "User" }. The assignment val e: Entity = User(7); the call e.tag() returns "User". This is polymorphic behaviour. The all-open plugin does this automatically; we model it. This structure is the basis of framework proxies.
Practice Write Open Entity + User
Define open class Entity(val id: Int) with open fun tag(): String = "Entity". Define class User(id: Int) : Entity(id) with override fun tag(): String = "User". In main, write val e: Entity = User(7) and println("${'$'}{e.tag()}:${'$'}{e.id}").
Starter code
// add the Entity and User classes
fun main() {
// print the polymorphic call
}Sample solution
open class Entity(val id: Int) {
open fun tag(): String = "Entity"
}
class User(id: Int) : Entity(id) {
override fun tag(): String = "User"
}
fun main() {
val e: Entity = User(7)
println("${e.tag()}:${e.id}")
}Expected output
User:7
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Which action can only be done by a plugin?
- Read annotations
- Make a class open Correct answer
- Return a list
- Generate a new file
Explanation: Making a class open modifies existing code; only a plugin can do it.
2 Complete the tag method
open class Entity(val id: Int) {
open fun ____(): String = "Entity"
}open class Entity(val id: Int) {
open fun tag(): String = "Entity"
}Explanation: tag() returns the entity type.
3 Match plugin concepts
| Term | Meaning |
|---|---|
all-open |
Makes a class open |
no-arg |
Adds a synthetic constructor |
IR |
Intermediate representation |
compose |
Transforms Composables |