refactor: remove virtual destructor from BasicIO to restore CRTP zero-overhead

[LHT129]

Summary

Remove the unnecessary virtual destructor from BasicIO<IOTmpl> (CRTP base class) to eliminate the vptr overhead and restore the zero-overhead static polymorphism design.

Changes

• src/io/basic_io.h: change virtual ~BasicIO() = default; to protected: ~BasicIO() = default;
• Remove override keyword from all 7 subclass destructors:
  • MemoryIO, BufferIO, MMapIO, AsyncIO, ReaderIO, MemoryBlockIO, NonContinuousIO

Rationale

BasicIO uses CRTP for static polymorphism — all *Impl methods are dispatched via static_cast<IOTmpl&>(*this). The virtual destructor was the only virtual function in the hierarchy, introducing an unnecessary vptr (8 bytes) per IO object. No IO object is ever deleted through a base pointer, so the virtual destructor serves no purpose.

Impact

• -8 bytes per IO object (vptr elimination)
• Eliminates unnecessary virtual dispatch overhead
• protected destructor prevents external deletion through base pointer at compile time

Fixes: #2397

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[gemini-code-assist]

Code Review

This pull request refactors the BasicIO class and its derived classes by replacing the public virtual destructor in BasicIO with a protected, non-virtual destructor. Consequently, the override specifier has been removed from the destructors of all derived classes, including AsyncIO, BufferIO, MemoryIO, and others. This design change prevents polymorphic deletion while eliminating virtual table overhead. There are no review comments, and I have no additional feedback to provide.

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[Copilot]

Pull request overview

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Refactors the CRTP BasicIO<IOTmpl> base class to remove its virtual destructor (and corresponding override destructors in derived classes) in order to eliminate vptr overhead and restore zero-overhead static polymorphism.

Changes:

• Make BasicIO’s destructor non-virtual and protected to prevent deletion via base pointer.
• Remove override from destructors across all BasicIO subclasses.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/io/basic_io.h	Makes BasicIO destructor protected and non-virtual, removing vptr/virtual dispatch.
src/io/reader_io.h	Removes override from ReaderIO destructor to match non-virtual base.
src/io/noncontinuous_io.h	Removes override from NonContinuousIO destructor to match non-virtual base.
src/io/mmap_io.h	Removes override from MMapIO destructor declaration.
src/io/memory_io.h	Removes override from MemoryIO inline destructor.
src/io/memory_block_io.h	Removes override from MemoryBlockIO destructor declaration.
src/io/buffer_io.h	Removes override from BufferIO inline destructor.
src/io/async_io.h	Removes override from AsyncIO destructor declaration.

[vsag-bot]

/label S-waiting-on-review
/waiting-on reviewer
/request-review @jiaweizone
/request-review @wxyucs
/request-review @inabao

[Copilot]

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated 1 comment.