xref: /aosp_15_r20/external/kotlinpoet/docs/kotlin-reflect.md (revision 3c321d951dd070fb96f8ba59e952ffc3131379a0)
1kotlin-reflect
2==============
3
4To generate source code from any [`KType`][k-type], including information that's not accessible to
5the builtin reflection APIs, KotlinPoet depends on [kotlin-reflect][kotlin-reflect]. `kotlin-reflect`
6can read the metadata of your classes and access this extra information. KotlinPoet can for an
7example, read the type parameters and their [variance][variance] from a generic `KType` and
8generate appropriate source code.
9
10`kotlin-reflect` is a relatively big dependency though and in some cases it is desirable to remove
11it from the final executable to save some space and/or simplify the proguard/R8 setup (for example
12for a Gradle plugin that generates Kotlin code). It is possible to do so and still use most of the
13KotlinPoet APIs:
14
15```kotlin
16dependencies {
17  implementation("com.squareup:kotlinpoet:<version>") {
18    exclude(module = "kotlin-reflect")
19  }
20}
21```
22
23The main APIs that require `kotlin-reflect` are [`KType.asTypeName()`][as-type-name] and
24[`typeNameOf<T>()`][type-name-of]. If you're calling one of these without `kotlin-reflect` in the
25classpath and the type is generic or has annotations you will get a crash.
26
27You can replace it with code that passes type parameters or annotations explicitly and doesn't
28need `kotlin-reflect`. For example:
29
30```kotlin
31// Replace
32// kotlin-reflect needed
33val typeName = typeNameOf<List<Int?>>()
34
35// With
36// kotlin-reflect not needed
37val typeName =
38  List::class.asClassName().parameterizedBy(Int::class.asClassName().copy(nullable = true))
39```
40
41 [k-type]: https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.reflect/-k-type/
42 [kotlin-reflect]: https://kotlinlang.org/docs/reflection.html#jvm-dependency
43 [variance]: https://kotlinlang.org/docs/generics.html#variance
44 [as-type-name]: https://square.github.io/kotlinpoet/1.x/kotlinpoet/kotlinpoet/com.squareup.kotlinpoet/as-type-name.html
45 [type-name-of]: https://square.github.io/kotlinpoet/1.x/kotlinpoet/kotlinpoet/com.squareup.kotlinpoet/type-name-of.html
46