Agent-skills-standard kotlin-language

Write idiomatic Kotlin 1.9+ with null safety, sealed classes, and expression syntax. Use when working with Kotlin null safety, data classes, sealed interfaces, extension functions, or migrating Java code to Kotlin. (triggers: **/*.kt, **/*.kts, val, var, ?., ?:, !!, data class, sealed, when, extension, lazy, lateinit, object)

install

source · Clone the upstream repo

git clone https://github.com/HoangNguyen0403/agent-skills-standard

Claude Code · Install into ~/.claude/skills/

T=$(mktemp -d) && git clone --depth=1 https://github.com/HoangNguyen0403/agent-skills-standard "$T" && mkdir -p ~/.claude/skills && cp -r "$T/skills/kotlin/kotlin-language" ~/.claude/skills/hoangnguyen0403-agent-skills-standard-kotlin-language && rm -rf "$T"

manifest: skills/kotlin/kotlin-language/SKILL.md

source content

Kotlin Language Patterns

Priority: P0 (CRITICAL)

Implementation Guidelines

Immutability: Use
```
val
```
by default. Only use
```
var
```
if mutation required locally.
Null Safety: Use
```
?
```
for nullable types. Use safe call
```
?.
```
and Elvis
```
?:
```
over
```
!!
```
.
Expressions: Prefer expression bodies
```
fun foo() = ...
```
for one-liners. Use
```
if
```
/
```
try
```
as expressions.
Classes: Use
```
data class
```
for DTOs. Use
```
sealed interface/class
```
for state hierarchies (e.g.,
```
Success
```
,
```
Error
```
,
```
Loading
```
). Access members as computed property rather than function.
Extension Functions: Prefer over utility classes (
```
StringUtil
```
). Keep private/internal if module-specific.
Named Arguments: Use for clarity, especially with booleans or multiple same-type params.
String Templates: Use
```
"$var"
```
over concatenation. Use
```
"""
```
for multiline strings (SQL/JSON).

Anti-Patterns

No !! Operator: Never use in production; prefer safe calls or requireNotNull.
No Java-isms: Use properties not get/set; prefer top-level functions over companion object statics.
No Lateinit Abuse: Prefer nullable types or lazy delegates instead.
No Silenced Errors: Never swallow exceptions without logging or handling.

References

Sealed Class, When Expression & Extension Examples