kotlin-patterns

Name: kotlin-patterns
Author: softspark

161stars21forks

How to install kotlin-patterns?

softspark/ai-toolkit/kotlin-patterns

$npx -y skills add softspark/ai-toolkit --skill kotlin-patterns

Installs into the current project.

Summary

Kotlin: coroutines, Flow, sealed/data classes, null safety, Ktor, Compose, KMP. Triggers: Kotlin, coroutine, Flow, suspend, Ktor, Jetpack Compose, KMP, kotlinx.

Files · 1

View on GitHub

SKILL.md

1	# Kotlin Patterns Skill
2
3	## Project Structure
4
5	### Gradle KTS Multi-Module Layout
6	```
7	project-root/
8	├── build.gradle.kts
9	├── settings.gradle.kts
10	├── gradle/libs.versions.toml
11	├── app/
12	│ ├── build.gradle.kts
13	│ └── src/{main,test}/kotlin/com/example/app/
14	├── domain/
15	│ └── src/main/kotlin/com/example/domain/
16	│ ├── model/
17	│ ├── repository/
18	│ └── usecase/
19	└── infrastructure/
20	└── src/main/kotlin/com/example/infra/
21	```
22
23	### settings.gradle.kts
24	```kotlin
25	rootProject.name = "my-project"
26	dependencyResolutionManagement {
27	versionCatalogs { create("libs") { from(files("gradle/libs.versions.toml")) } }
28	}
29	include(":app", ":domain", ":infrastructure")
30	```
31
32	### Module build.gradle.kts
33	```kotlin
34	plugins {
35	alias(libs.plugins.kotlin.jvm)
36	alias(libs.plugins.kotlin.serialization)
37	}
38	dependencies {
39	implementation(project(":domain"))
40	implementation(libs.kotlinx.coroutines.core)
41	testImplementation(libs.bundles.testing)
42	}
43	kotlin { jvmToolchain(21) }
44	```
45
46	---
47
48	## Idioms / Code Style
49
50	### Data Classes + Value Classes
51	```kotlin
52	data class User(
53	val id: UserId,
54	val name: String,
55	val email: String,
56	val role: Role = Role.USER,
57	) {
58	init {
59	require(name.isNotBlank()) { "Name must not be blank" }
60	require(email.contains("@")) { "Invalid email format" }
61	}
62	}
63
64	@JvmInline
65	value class UserId(val value: String) // Zero-overhead type-safe ID
66	enum class Role { ADMIN, USER, GUEST }
67	```
68
69	### Sealed Interfaces for Domain Modeling
70	```kotlin
71	sealed interface PaymentResult {
72	data class Success(val transactionId: String, val amount: Money) : PaymentResult
73	data class Declined(val reason: String) : PaymentResult
74	data class Error(val exception: Throwable) : PaymentResult
75	}
76
77	// Exhaustive when -- compiler enforces all branches
78	fun handlePayment(result: PaymentResult): String = when (result) {
79	is PaymentResult.Success -> "Paid: ${result.amount}"
80	is PaymentResult.Declined -> "Declined: ${result.reason}"
81	is PaymentResult.Error -> "Error: ${result.exception.message}"
82	}
83	```
84
85	### Extension Functions
86	```kotlin
87	fun String.toSlug(): String =
88	lowercase().replace(Regex("[^a-z0-9\\s-]"), "").replace(Regex("\\s+"), "-").trim('-')
89
90	// Scoped extensions -- visible only inside containing class
91	class OrderService {
92	private fun Order.totalWithTax(): Money = total * (1 + taxRate)
93	}
94	```
95
96	### Null Safety
97	```kotlin
98	fun getDisplayName(user: User?): String =
99	user?.name?.takeIf { it.isNotBlank() } ?: "Anonymous"
100
101	fun processEmail(email: String?) { email?.let { sendWelcomeEmail(it) } }
102
103	fun loadConfig(path: String?): Config {
104	val resolved = requireNotNull(path) { "Config path must not be null" }
105	return parseConfig(resolved)
106	}
107	```
108
109	### Scope Functions
110
111	\| Function \| Ref \| Returns \| Use case \|
112	\|----------\|-----\|---------\|----------\|
113	\| `let` \| `it` \| Lambda result \| Null check + transform \|
114	\| `run` \| `this` \| Lambda result \| Config + compute \|
115	\| `apply` \| `this` \| Object itself \| Object initialization \|
116	\| `also` \| `it` \| Object itself \| Side effects \|
117
118	```kotlin
119	val conn = Connection().apply { host = "localhost"; port = 5432 }
120	fun createUser(req: CreateUserRequest): User =
121	userRepository.save(req.toUser()).also { logger.info("Created: ${it.id}") }
122	```
123
124	### Type-Safe Builders (DSL)
125	```kotlin
126	fun html(block: HtmlBuilder.() -> Unit): String = HtmlBuilder().apply(block).build()
127
128	val page = html {
129	head { title("My Page") }
130	body { p("Hello, world!") }
131	}
132	```
133
134	---
135
136	## Error Handling
137
138	### Result<T> and runCatching
139	```kotlin
140	fun findUser(id: UserId): Result<User> = runCatching {
141	userRepository.findById(id) ?: throw UserNotFoundException(id)
142	}
143
144	fun getUserDisplayName(id: UserId): String =
145	findUser(id).map { it.name }.recover { "Unknown User" }.getOrThrow()
146
147	fun handleLookup(id: UserId): Response = findUser(id).fold(
148	onSuccess = { Response.ok(it) },
149	onFailure = { Response.notFound(it.message) },
150	)
151	```
152
153	### Sealed Class Error Hierarchy
154	```kotlin
155	sealed class DomainError(override val message: String) : Exception(message) {
156	data class NotFound(val resource: String, val id: String) : DomainError("$resource not found: $id")
157	data class Validation(val field: String, val reason: String) : DomainError("Invalid $field: $reason")
158	data class Conflict(val detail: String) : DomainError("Conflict: $detail")
159	}
160
161	fun handleError(error: DomainError): Response = when (error) {
162	is DomainError.NotFound -> Response.status(404).body(error.message)
163	is DomainError.Validation -> Response.status(422).body(error.message)
164	is DomainError.Conflict -> Response.status(409).body(error.message)
165	}
166	```
167
168	### Preconditions
169	```kotlin
170	fun transferMoney(from: Account, to: Account, amount: Money) {

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kotlin-patterns

161stars21forks

View on GitHub

How to install kotlin-patterns?

softspark/ai-toolkit/kotlin-patterns

$npx -y skills add softspark/ai-toolkit --skill kotlin-patterns

Installs into the current project.

Summary

Kotlin: coroutines, Flow, sealed/data classes, null safety, Ktor, Compose, KMP. Triggers: Kotlin, coroutine, Flow, suspend, Ktor, Jetpack Compose, KMP, kotlinx.

Files · 1

View on GitHub

SKILL.md

1	# Kotlin Patterns Skill
2
3	## Project Structure
4
5	### Gradle KTS Multi-Module Layout
6	```
7	project-root/
8	├── build.gradle.kts
9	├── settings.gradle.kts
10	├── gradle/libs.versions.toml
11	├── app/
12	│ ├── build.gradle.kts
13	│ └── src/{main,test}/kotlin/com/example/app/
14	├── domain/
15	│ └── src/main/kotlin/com/example/domain/
16	│ ├── model/
17	│ ├── repository/
18	│ └── usecase/
19	└── infrastructure/
20	└── src/main/kotlin/com/example/infra/
21	```
22
23	### settings.gradle.kts
24	```kotlin
25	rootProject.name = "my-project"
26	dependencyResolutionManagement {
27	versionCatalogs { create("libs") { from(files("gradle/libs.versions.toml")) } }
28	}
29	include(":app", ":domain", ":infrastructure")
30	```
31
32	### Module build.gradle.kts
33	```kotlin
34	plugins {
35	alias(libs.plugins.kotlin.jvm)
36	alias(libs.plugins.kotlin.serialization)
37	}
38	dependencies {
39	implementation(project(":domain"))
40	implementation(libs.kotlinx.coroutines.core)
41	testImplementation(libs.bundles.testing)
42	}
43	kotlin { jvmToolchain(21) }
44	```
45
46	---
47
48	## Idioms / Code Style
49
50	### Data Classes + Value Classes
51	```kotlin
52	data class User(
53	val id: UserId,
54	val name: String,
55	val email: String,
56	val role: Role = Role.USER,
57	) {
58	init {
59	require(name.isNotBlank()) { "Name must not be blank" }
60	require(email.contains("@")) { "Invalid email format" }
61	}
62	}
63
64	@JvmInline
65	value class UserId(val value: String) // Zero-overhead type-safe ID
66	enum class Role { ADMIN, USER, GUEST }
67	```
68
69	### Sealed Interfaces for Domain Modeling
70	```kotlin
71	sealed interface PaymentResult {
72	data class Success(val transactionId: String, val amount: Money) : PaymentResult
73	data class Declined(val reason: String) : PaymentResult
74	data class Error(val exception: Throwable) : PaymentResult
75	}
76
77	// Exhaustive when -- compiler enforces all branches
78	fun handlePayment(result: PaymentResult): String = when (result) {
79	is PaymentResult.Success -> "Paid: ${result.amount}"
80	is PaymentResult.Declined -> "Declined: ${result.reason}"
81	is PaymentResult.Error -> "Error: ${result.exception.message}"
82	}
83	```
84
85	### Extension Functions
86	```kotlin
87	fun String.toSlug(): String =
88	lowercase().replace(Regex("[^a-z0-9\\s-]"), "").replace(Regex("\\s+"), "-").trim('-')
89
90	// Scoped extensions -- visible only inside containing class
91	class OrderService {
92	private fun Order.totalWithTax(): Money = total * (1 + taxRate)
93	}
94	```
95
96	### Null Safety
97	```kotlin
98	fun getDisplayName(user: User?): String =
99	user?.name?.takeIf { it.isNotBlank() } ?: "Anonymous"
100
101	fun processEmail(email: String?) { email?.let { sendWelcomeEmail(it) } }
102
103	fun loadConfig(path: String?): Config {
104	val resolved = requireNotNull(path) { "Config path must not be null" }
105	return parseConfig(resolved)
106	}
107	```
108
109	### Scope Functions
110
111	\| Function \| Ref \| Returns \| Use case \|
112	\|----------\|-----\|---------\|----------\|
113	\| `let` \| `it` \| Lambda result \| Null check + transform \|
114	\| `run` \| `this` \| Lambda result \| Config + compute \|
115	\| `apply` \| `this` \| Object itself \| Object initialization \|
116	\| `also` \| `it` \| Object itself \| Side effects \|
117
118	```kotlin
119	val conn = Connection().apply { host = "localhost"; port = 5432 }
120	fun createUser(req: CreateUserRequest): User =
121	userRepository.save(req.toUser()).also { logger.info("Created: ${it.id}") }
122	```
123
124	### Type-Safe Builders (DSL)
125	```kotlin
126	fun html(block: HtmlBuilder.() -> Unit): String = HtmlBuilder().apply(block).build()
127
128	val page = html {
129	head { title("My Page") }
130	body { p("Hello, world!") }
131	}
132	```
133
134	---
135
136	## Error Handling
137
138	### Result<T> and runCatching
139	```kotlin
140	fun findUser(id: UserId): Result<User> = runCatching {
141	userRepository.findById(id) ?: throw UserNotFoundException(id)
142	}
143
144	fun getUserDisplayName(id: UserId): String =
145	findUser(id).map { it.name }.recover { "Unknown User" }.getOrThrow()
146
147	fun handleLookup(id: UserId): Response = findUser(id).fold(
148	onSuccess = { Response.ok(it) },
149	onFailure = { Response.notFound(it.message) },
150	)
151	```
152
153	### Sealed Class Error Hierarchy
154	```kotlin
155	sealed class DomainError(override val message: String) : Exception(message) {
156	data class NotFound(val resource: String, val id: String) : DomainError("$resource not found: $id")
157	data class Validation(val field: String, val reason: String) : DomainError("Invalid $field: $reason")
158	data class Conflict(val detail: String) : DomainError("Conflict: $detail")
159	}
160
161	fun handleError(error: DomainError): Response = when (error) {
162	is DomainError.NotFound -> Response.status(404).body(error.message)
163	is DomainError.Validation -> Response.status(422).body(error.message)
164	is DomainError.Conflict -> Response.status(409).body(error.message)
165	}
166	```
167
168	### Preconditions
169	```kotlin
170	fun transferMoney(from: Account, to: Account, amount: Money) {

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