Feat/small pimpl

[Alex2772]

small pimpl that might be required by #666.

[gemini-code-assist]

Summary of Changes

Hello @Alex2772, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a significant new utility, small_pimpl, designed to enhance performance and reduce dynamic memory allocations for PIMPL (Pointer to Implementation) idioms. By intelligently deciding whether to store the implementation object on the stack or heap based on its size, it provides a more efficient alternative to std::unique_ptr for certain use cases. This change is accompanied by robust testing to ensure its correctness and reliability, and minor build system adjustments to integrate these new tests.

Highlights

• New small_pimpl Utility: Introduced a new small_pimpl class template that provides a small buffer optimized PIMPL implementation. This utility stores the implementation object inline on the stack if its size is less than or equal to a specified StackSize, falling back to heap allocation for larger objects.
• Automatic Storage Management: The small_pimpl automatically determines whether to allocate the concrete type on the stack or heap, optimizing for performance by avoiding dynamic allocations for small objects. It uses std::variant internally to manage storage and dispatch ownership/destructors.
• Comprehensive Test Coverage: Added a dedicated test suite (SmallPimplTest.cpp) to thoroughly validate the small_pimpl functionality, including allocation decisions, method invocation, destructor calls, and correct handling of copy and move semantics for both stack-allocated and heap-allocated types.
• Build System Update: Modified the .vscode/tasks.json configuration to include 'Tests' in the default build targets, ensuring that the newly added tests are part of the standard build process.
• Documentation Formatting: Updated the documentation in APimpl.h to use a more modern Markdown-like list format for details sections, improving readability.

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Changelog

• .vscode/tasks.json
  • Added 'Tests' to the build targets for the 'build' task.
• aui.core/src/AUI/Util/APimpl.h
  • Updated documentation formatting for list items from HTML <ul><li> to Markdown-style -.
• aui.core/src/AUI/Util/SmallPimpl.h
  • Added small_pimpl class template for small buffer optimized PIMPL implementation.
  • Implemented internal ControlBlock for type erasure and handling of Interface* to T* conversions.
  • Provided StackAllocated and HeapAllocated internal structs for managing storage based on object size.
  • Defined constructors, copy/move semantics, and accessors (operator->, operator*, ptr()) for the small_pimpl.
• aui.core/tests/SmallPimplTest.cpp
  • Added a new test file for small_pimpl functionality.
  • Included tests for allocation decisions (stack vs. heap) based on object size.
  • Verified correct invocation of methods through the small_pimpl interface using GMock.
  • Confirmed proper destructor calls for both stack and heap-allocated objects.
  • Tested copy and move semantics for various concrete types (copy-only, move-only).

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[gemini-code-assist]

Code Review

This pull request introduces a new small_pimpl utility, which provides a small buffer optimized PIMPL implementation, similar to std::unique_ptr but with optional inline storage for small objects. This is a valuable addition for optimizing memory usage and reducing heap allocations. The PR also includes comprehensive unit tests for the new utility, covering allocation decisions, method invocation, and copy/move semantics. Additionally, the Doxygen documentation in APimpl.h has been updated for better readability, and the build configuration has been extended to include tests.

During the review, I've identified a few issues related to pointer handling within the small_pimpl implementation and an incorrect assertion in the move test. Addressing these will ensure the correctness and robustness of the new utility.

[Alex2772]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces a small_pimpl utility, which is a great addition for performance optimization. The implementation is well-structured, leveraging modern C++ features like std::variant for storage. However, I've identified a few critical issues concerning copy and move semantics, particularly within the StackAllocated implementation, and missing assignment operators which could lead to undefined behavior or compilation failures. I've provided detailed comments and suggestions to address these issues. Additionally, I've included a couple of minor suggestions to enhance the class's usability and style.

[Alex2772]

/home/alex2772/CLionProjects/aui/cmake-build-relwithdebinfo/bin/Benchmarks --benchmark_filter=.*
2026-02-20T02:56:27+03:00
Running /home/alex2772/CLionProjects/aui/cmake-build-relwithdebinfo/bin/Benchmarks
Run on (32 X 5086.18 MHz CPU s)
CPU Caches:
  L1 Data 32 KiB (x16)
  L1 Instruction 32 KiB (x16)
  L2 Unified 512 KiB (x16)
  L3 Unified 32768 KiB (x2)
Load Average: 14.71, 6.43, 3.65
***WARNING*** CPU scaling is enabled, the benchmark real time measurements may be noisy and will incur extra overhead.
***WARNING*** ASLR is enabled, the results may have unreproducible noise in them.
----------------------------------------------------------------------------------------------------------
Benchmark                                                                Time             CPU   Iterations
----------------------------------------------------------------------------------------------------------
SmallPimpl_Allocation<aui::small_pimpl<ITest, 128>, SmallImpl>        2.12 ns         2.11 ns    333858259
SmallPimpl_Allocation<std::function<void()>, SmallImpl>               8.59 ns         8.55 ns     83463874
SmallPimpl_Allocation<aui::small_pimpl<ITest, 128>, MediumImpl>       3.22 ns         3.20 ns    220340695
SmallPimpl_Allocation<std::function<void()>, MediumImpl>              8.36 ns         8.33 ns     82877739
SmallPimpl_Allocation<aui::small_pimpl<ITest, 128>, BigImpl>          51.1 ns         50.7 ns     14034323
SmallPimpl_Allocation<std::function<void()>, BigImpl>                 52.6 ns         52.4 ns     12969600
SmallPimpl_Copy<aui::small_pimpl<ITest, 128>, SmallImpl>              4.24 ns         4.20 ns    166740471
SmallPimpl_Copy<std::function<void()>, SmallImpl>                     10.2 ns         10.1 ns     70236187
SmallPimpl_Copy<aui::small_pimpl<ITest, 128>, MediumImpl>             4.22 ns         4.20 ns    166158461
SmallPimpl_Copy<std::function<void()>, MediumImpl>                    10.7 ns         10.7 ns     69750309
SmallPimpl_Copy<aui::small_pimpl<ITest, 128>, BigImpl>                26.6 ns         26.5 ns     26582109
SmallPimpl_Copy<std::function<void()>, BigImpl>                       26.0 ns         25.9 ns     27228219
SmallPimpl_Invoke<aui::small_pimpl<ITest, 128>, SmallImpl>            1.16 ns         1.15 ns    609427092
SmallPimpl_Invoke<std::function<void()>, SmallImpl>                   1.20 ns         1.19 ns    598789144
SmallPimpl_Invoke<aui::small_pimpl<ITest, 128>, MediumImpl>           1.15 ns         1.15 ns    607650646
SmallPimpl_Invoke<std::function<void()>, MediumImpl>                  1.39 ns         1.38 ns    508979367
SmallPimpl_Invoke<aui::small_pimpl<ITest, 128>, BigImpl>              1.44 ns         1.42 ns    511851310
SmallPimpl_Invoke<std::function<void()>, BigImpl>                     1.17 ns         1.17 ns    597973846