# Swift Error Handling

> Standards for Throwing Functions, Result Type, and Never

- Skill: `fierzone/swift-error-handling` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add fierzone/swift-error-handling`
- Raw SKILL.md: https://api.skillmd.com/api/skills/fierzone/swift-error-handling/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: fierzone (https://skillmd.com/u/fierzone)
- Updated: 2026-09-10
- Page: https://skillmd.com/skills/fierzone/swift-error-handling

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# Swift Error Handling

## **Priority: P0**

## Implementation Guidelines

### Throwing Functions

- **Propagate Errors**: Use `throws` for recoverable errors.
- **Do-Catch**: Handle errors close to source with specific catch blocks.
- **Error Types**: Define custom errors as enums conforming to `Error`.

### Result Type

- **Async Alternatives**: Use `Result<Success, Failure>` for callback-based APIs.
- **Transformations**: Use `.map()`, `.flatMap()` for functional composition.
- **Conversion**: Use `.get()` to convert `Result` to throwing.

### Never Type

- **Fatalisms**: Use `Never` return type for functions that never return.
- **Preconditions**: `fatalError()`, `preconditionFailure()` for programmer errors.

## Anti-Patterns

- **Force Try**: `**No try!**: Use try? or do-catch.`
- **Silent Failures**: `**No try? without nil check**: Handle or log.`
- **String Errors**: `**No Error(message)**: Use typed errors.`

## References

- [Error Types & Result](references/implementation.md)