How do you unwrap Swift optionals?

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There are many similarities and just a handful of differences.

(Regular) Optionals

  • Declaration: var opt: Type?

  • Unsafely unwrapping: let x = opt!.property // error if opt is nil

  • Safely testing existence : if opt != nil { ... someFunc(opt!) ... } // no error

  • Safely unwrapping via binding: if let x = opt { ... someFunc(x) ... } // no error

  • Safely chaining: var x = opt?.property // x is also Optional, by extension

  • Safely coalescing nil values: var x = opt ?? nonOpt

Implicitly Unwrapped Optionals

  • Declaration: var opt: Type!

  • Unsafely unwrapping (implicit): let x = opt.property // error if opt is nil

    • Unsafely unwrapping via assignment:
      let nonOpt: Type = opt // error if opt is nil

    • Unsafely unwrapping via parameter passing:
      func someFunc(nonOpt: Type) ...
      someFunc(opt) // error if opt is nil

  • Safely testing existence: if opt != nil { ... someFunc(opt) ... } // no error

  • Safely chaining: var x = opt?.property // x is also Optional, by extension

  • Safely coalescing nil values: var x = opt ?? nonOpt

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