android-error-handling

Files (1)

• SKILL.md

SKILL.md (first lines)

# Android / KMP Error Handling

## Result Wrapper (`core:domain`)

A generic, typed Result that works across all layers — data, domain, presentation, validation, anywhere a function can succeed or fail with a typed error.

```kotlin
interface Error

sealed interface Result<out D, out E : Error> {
    data class Success<out D>(val data: D) : Result<D, Nothing>
    data class Error<out E : com.example.Error>(val error: E) : Result<Nothing, E>
}

typealias EmptyResult<E> = Result<Unit, E>
```

---

## Extension Helpers (`core:domain`)

These live alongside the `Result` definition:

```kotlin
inline fun <T, E : Error, R> Result<T, E>.map(
    map: (T) -> R
): Result<R, E> {
    return when (this) {
        is Result.Error -> Result.Error(error)
        is Result.Success -> Result.Success(map(this.data))
    }
}

inline fun <T, E : Error> Result<T, E>.onSuccess(
    action: (T) -> Unit
): Result<T, E> {
    return when (this) {
        is Result.Error -> this
        is Result.Success -> {
            action(this.data)
            this
        }
    }
}

inline fun <T, E : Error> Result<T, E>.onFailure(
    action: (E) -> Unit
): Result<T, E> {
    return when (this) {
        is Result.Error -> {
            action(error)
            this
        }
        is Result.Success -> this
    }
}

fun <T, E : Error> Result<T, E>.asEmptyResult(): EmptyResult<E> {
    return map { }
}
```

All helpers return `Result` so they can be chained:
```kotlin
repository.saveNote(note)
    .onSuccess { /* update UI */ }
    .onFailure { /* show error */ }
    .asEmptyResult()
```

---

## Shared Error Types (`core:domain`)

### DataError

```kotlin
sealed interface DataError : Error {
    enum class Network : DataError {
        BAD_REQUEST,
        REQUEST_TIMEOUT,
        UNAUTHORIZED,
        FORBIDDEN,
        NOT_FOUND,
        CONFLICT,
        TOO_MANY_REQUESTS,
        NO_INTERNET,
        PAYLOAD_TOO_LARGE,
        SERVER_ERROR,
        SERVICE_UNAVAILABLE,
        SERIALIZATION,
        UNKNOWN
    }

    enum class Local : DataError {
        DISK_FULL,
        NOT_FOUND,
        UNKNOWN
    }
}
```

### Feature-Specific Errors

Features define their own error types by implementing `Error`:

```kotlin
enum class PasswordValidationError : Error {
    TOO_SHORT,
    NO_UPPERCASE,
    NO_DIGIT
}

// Used with Result — always a single error, not a list:
fun validatePassword(pw: String): EmptyResult<PasswordValidationError>
```

Multiple validation errors are not supported — always return a single error type per Result.

From kvithayathil/agent-resources, AGPL-3.0.

More from kvithayathil/agent-resources