> swift-language

Standards for Optionals, Protocols, Extensions, and Type Safety. Use when working with Swift Optionals, Protocols, Extensions, or type-safe APIs. (triggers: **/*.swift, protocol, extension, optional, guard, enum)

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SKILL.mdswift-language

Swift Language Standards

Priority: P0

Implementation Guidelines

Optionals & Safety

  • Never Force Unwrap: Use guard let, if let, or nil coalescing (??).
  • Nil Comparison: Use value != nil instead of if let _ = value.
  • Implicitly Unwrapped: Avoid Type!. Use proper Type?.

Protocols & Extensions

  • Protocol Composition: Prefer struct + protocols over class inheritance.
  • Extensions: Use for conformance (extension MyType: Codable), not storage.
  • Protocol Witnesses: Explicitly implement all required members.

Type Safety

  • Avoid Any: Use generics or associated types instead.
  • Enums: Prefer enums with associated values over multiple Optionals.
  • Value Types: Default to struct unless reference semantics needed.

Anti-Patterns

  • Force Unwrapping: **No ! operator**: Use safe unwrapping.
  • Sentinel Values: **No -1 for failure**: Use Optional.
  • as! Casting: **No Force Cast**: Use conditional cast (as?).

References

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first seenMar 17, 2026
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┌ repo

HoangNguyen0403/agent-skills-standard
by HoangNguyen0403
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┌ tags

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