Migration Patterns

Migration Patterns

Generic, non-repo-specific migration references retained as background reading.

Authority note. This repo's ObjC → Swift migration is governed by docs/migration/playbook.md, plus agents/xcodebuild/SKILL.md (build-error triage) and agents/review/SKILL.md (review checklist). Those are derived from actual build failures in this codebase. Where the generic objc-to-swift.md below disagrees with them, the playbook wins. See "Known conflicts" for the specific points.

Available guides

Known conflicts between objc-to-swift.md and this repo

Four points where following the generic guide would break this SDK:

1. @objc naming. The guide only ever shows bare @objc class Foo: NSObject. The parenthesized form @objc(PBMFoo) never appears in it. This repo has 153 @objc(PBM…) declarations, and they exist to preserve the shipped ObjC API name while the Swift type drops the prefix. Omitting it silently renames a public class. See playbook "Naming convention".

2. Value types. The guide advises converting NSObject subclasses to structs (objc-to-swift.md:25, :121). Phase 1–3 ORTB twins must stay @objc NSObject subclasses because ObjC parameter builders still consume them — playbook Gap 4.

3. Bridging headers. The guide makes them central. The PrebidMobile framework target has no bridging header and cannot use one; only the test target does. See playbook Gap 8 on private-header invisibility in framework builds.

4. The Swift→ObjC import. The guide says #import "ProjectName-Swift.h". This repo must use #import "SwiftImport.h", a conditional shim — a direct import compiles under CocoaPods and fails under SPM.

Also absent from the guide entirely: NSCopying (playbook records that .copy() crashes at runtime on twins that omit it) and the @_spi(PBMInternal) propagation rules.

Why this repo stays on XCTest

Recorded so the question does not get reopened. xctest-to-swift-testing.md:433-441 disqualifies this repo on two of its own criteria: shared test infrastructure via XCTestCase subclassing, and ObjC test helpers that depend on XCTestCase. Beyond that, the .xctestplan registry, the ObjC test bridging header, and the flaky-test isolation procedure in agents/xcodebuild/SKILL.md all assume XCTest's Class/method addressing.

Note in particular that the generic advice to "migrate tests first for a safety net" is wrong here — the XCTest suite is the safety net for the ObjC → Swift work, and it gates every migration PR (./scripts/testPrebidMobile.sh --latest --quick). Dismantling it first would remove the gate before the risky work begins.

References

• Migrating a test from XCTest
• Swift and Objective-C in the same project