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Swift Academy · Lesson

Migrating to Strict Concurrency

Adopt Swift 6 concurrency checking incrementally.

What Is Strict Concurrency?

Strict concurrency checking makes the compiler diagnose every potential data race at compile time.

In Swift 6 language mode it is on by default; in Swift 5 mode you opt in incrementally.

The Three Checking Levels

The -strict-concurrency flag has three levels: minimal (default in Swift 5), targeted (checks code already using concurrency), and complete (full Swift 6 style checking).

// Build settings example
// SWIFT_STRICT_CONCURRENCY = complete

All lessons in this course

  1. The Data Race Problem
  2. The Sendable Protocol
  3. Actor Isolation and nonisolated
  4. Migrating to Strict Concurrency
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