# Refactor a Legacy Objective-C Module with Atlas in 2026 > Atlas helps Objective-C developers refactor legacy modules by mapping public surfaces, pinning behavior with `xcodebuild test`, and applying structural changes safely. Atlas empowers Objective-C developers in 2026 to refactor legacy modules by leveraging the familiar toolchain, including `XCTest (xcodebuild test)` for behavior pinning, `CocoaPods` for dependency management, and `clang-format` for code style, all while ensuring no breaking changes to callers. It maps public surfaces, pins existing behavior, and applies structural changes with precise, context-aware patches. ## Key takeaways - Atlas uses `lsp findReferences` to map all Objective-C callsites, including those from Swift bridging headers. - Behavior is pinned by running `XCTest` suites with `xcodebuild test` before and after each change. - `apply_patch` ensures safe Objective-C code restructuring by validating context lines, preventing drift. - Atlas integrates `clang-format` for consistent Objective-C style and `git` for robust version control. - Every Atlas tool call and file edit is permission-gated and presented as a unified diff for approval. - The `todowrite` tool tracks remaining Objective-C callsite migrations, preventing incomplete refactors. ## How Atlas Maps Objective-C Module Interfaces for Refactoring In 2026, Atlas begins an Objective-C module refactor by meticulously mapping its public interface, using the `lsp` tool's `documentSymbol` operation to identify every exported declaration in `.h` and `.m` files. This initial step ensures a comprehensive understanding of the module's external contract before any changes are considered. Refactoring an Objective-C module without breaking its callers requires a precise understanding of its public surface. Atlas achieves this by integrating with the Language Server Protocol (LSP) through its `lsp` tool. For a module defined across `MyModule.h` and `MyModule.m`, Atlas will first use `lsp documentSymbol` to enumerate all publicly accessible methods, properties, and functions. Following this, Atlas performs `lsp findReferences` on each identified symbol. This operation is critical for Objective-C projects, especially those with `CocoaPods` dependencies or bridging headers for Swift, as it accurately identifies every single callsite across the entire codebase, including those in other modules or even Swift files that import the Objective-C header. This comprehensive mapping prevents silent breakage by ensuring all callers are accounted for and tracked in a `todowrite` list, guaranteeing a complete migration. ## Pinning Objective-C Module Behavior with XCTest Before Refactoring Before any structural changes are made to an Objective-C module, Atlas prioritizes pinning its existing behavior by running `XCTest` suites with `xcodebuild test` to establish a green baseline. This crucial step, performed in 2026, ensures that the module's functionality remains identical throughout the refactoring process, preventing regressions. The most significant risk in refactoring a legacy Objective-C module is inadvertently altering its behavior. Atlas mitigates this by enforcing a 'pin behavior first' principle. Using the `bash` tool, Atlas executes the project's `XCTest` suite via the command `xcodebuild test -workspace MyProject.xcworkspace -scheme MyModuleTests`. It records the output, establishing a 'green baseline' of passing tests. This baseline serves as the immutable contract for the module's behavior. After each incremental change during the refactor, Atlas re-runs `xcodebuild test`. If any test fails, Atlas immediately flags the issue, allowing the developer to address the regression before proceeding. This iterative testing approach, deeply integrated with the Objective-C testing ecosystem, provides continuous validation and confidence throughout the refactoring lifecycle. ## Safe Objective-C Code Restructuring with Atlas's apply_patch Tool Atlas facilitates safe restructuring of Objective-C code in 2026 using its `apply_patch` tool, which anchors changes on context lines and refuses to apply against drifted files. This ensures that modifications to `.h` and `.m` pairs, or even category files like `MyCategory+Extension.m`, are precise and do not corrupt the codebase. Once the public surface is mapped and behavior is pinned, Atlas proceeds with the actual restructuring using its `apply_patch` tool. Unlike simple line-based edits, `apply_patch` is designed for robust, context-aware modifications. When Atlas proposes a change to an Objective-C file, such as moving a method from one `.m` file to another or adjusting an `ARC` property declaration in a `.h` file, the patch includes surrounding context lines. If the target file has drifted,meaning its content no longer matches the patch's expected context,`apply_patch` will fail with a `Failed to find context` error. This prevents applying changes to an outdated version of the file, safeguarding against unintended code corruption. Atlas computes a unified diff for every proposed edit, presenting it for developer approval before writing, ensuring full transparency and control over every modification to your Objective-C codebase. ## Ensuring Objective-C Code Quality and Review with Atlas Atlas integrates direct with Objective-C's `clang-format` and `git` in 2026 to ensure high code quality and a robust review process during refactoring. Every change is formatted, diffed, and can be staged and committed, providing a clear audit trail and easy rollback capabilities. Maintaining code quality and facilitating review are paramount during an Objective-C refactor. Atlas automatically runs `clang-format` over any changed `.h` and `.m` files, ensuring consistent style across the module. Before any file is written, Atlas generates a unified diff, which is presented to the developer for explicit approval. This granular control allows developers to review every line change, ensuring accuracy and preventing unwanted modifications. Furthermore, Atlas leverages `git` capabilities: it reads branches, status, and diffs, and can stage and create commits on your behalf. It also snapshots file changes as `git` patches, allowing edits to be easily diffed and rolled back if necessary. This comprehensive approach to review and version control, combined with permission-gated tool calls and a read-only plan agent, provides unparalleled safety and transparency for Objective-C developers. ## Steps 1. Initialize Atlas in your Objective-C project by running it within a directory containing your `.xcodeproj` or `.xcworkspace` file, allowing it to index your `.h` and `.m` pairs and `Podfile` dependencies. 2. Map the module's public surface: Use `atlas lsp documentSymbol` on the module's primary header (`MyModule.h`) to identify exported declarations, then `atlas lsp findReferences` on each symbol to enumerate all callers across your Objective-C and bridged Swift code. 3. Pin existing behavior: Execute `atlas bash xcodebuild test -workspace MyProject.xcworkspace -scheme MyModuleTests` to run your `XCTest` suite and record a green baseline of passing tests before any changes are made. 4. Restructure incrementally: Draft a plan in Atlas's read-only plan agent to move or modify Objective-C code. Atlas will use `apply_patch` to propose changes, anchoring on context lines and failing if the file has drifted. 5. Approve and apply changes: Review the unified diff presented by Atlas for each proposed `apply_patch` operation. Approve the changes to write them to your `.h` and `.m` files. 6. Validate behavior: After each `apply_patch` lands, immediately re-run `atlas bash xcodebuild test -workspace MyProject.xcworkspace -scheme MyModuleTests` to ensure the module's behavior remains unchanged and no regressions have been introduced. 7. Track remaining work: Use `atlas todowrite` to maintain a list of remaining callsites that need migration, ensuring no partially refactored Objective-C module is mistakenly considered complete. 8. Format and commit: Allow Atlas to run `clang-format` over the changed `.h` and `.m` files, then use Atlas to stage and create a `git` commit for the refactored changes. ## FAQ ### How does Atlas handle Objective-C header and implementation files during refactoring? Atlas understands Objective-C's `.h` and `.m` file pairs, indexing them by AST declarations using tree-sitter. It applies structural changes to both files, ensuring consistency and correctly identifying references across them, even for category files like `MyClass+Category.m`. ### Can Atlas refactor Objective-C codebases that use CocoaPods? Yes, Atlas is designed to work with Objective-C projects that use `CocoaPods`. It reads your `Podfile` and indexes the pods, allowing `lsp findReferences` to accurately locate callsites within your dependencies and across your entire workspace. ### How does Atlas ensure no breaking changes for Swift code calling Objective-C? Atlas uses `lsp findReferences` to identify all callsites, including those from Swift through bridging headers. It can also annotate nullability on Objective-C headers, ensuring Swift sees the correct optionality and preventing unexpected runtime issues after refactoring. ### What if my Objective-C module doesn't have XCTest coverage? While Atlas can help add `XCTest` cases behind a permission prompt, the 'pin behavior first' workflow is most effective with existing tests. If coverage is low, Atlas will still map callsites and apply patches safely, but behavioral validation will rely more on manual review. ### How does Atlas prevent accidental changes to my Objective-C project? Atlas employs several safety mechanisms: a read-only plan agent, permission-gated tool calls, unified diffs for every file edit requiring approval, and `apply_patch`'s context-anchoring to prevent applying changes to drifted files. It also snapshots changes as `git` patches for easy rollback. ### Can Atlas help with Objective-C ARC migration or nullability annotations? While the primary focus is refactoring, Atlas's understanding of Objective-C AST declarations and `lsp` capabilities means it can assist with tasks like annotating nullability on headers for better Swift bridging, and its `apply_patch` tool can be used for structural changes related to ARC. ### How does Atlas integrate with my existing Objective-C development workflow? Atlas is terminal-native and integrates directly into your existing `git` and `xcodebuild` workflow. It uses your project's `.xcodeproj` or `.xcworkspace`, respects `clang-format` configurations, and allows you to switch models and providers on the fly, fitting into your daily development cycle. --- Canonical HTML: https://runatlas.sh/resources/stacks/refactor-a-legacy-module-in-objective-c Source of truth: aeo_pages row `/resources/stacks/refactor-a-legacy-module-in-objective-c` (segment: Stacks) (this file is generated from it, never hand-edited). Licence: Atlas is proprietary with a free core. It is not open source and there is no public source repository.