COMP: Move inline = default destructors to .cxx for 30 exported classes

[thewtex]

Non-template exported classes with ~ClassName() override = default; inline in the header have hidden D1Ev/D0Ev destructor thunks under -fvisibility-inlines-hidden, even when the class vtable and typeinfo remain exported. This breaks dynamic_cast across DSO boundaries in shared library builds.

Moving the destructor definition out of line to the .cxx file ensures it is compiled in exactly one translation unit, giving it default (exported) visibility and correctly anchoring all destructor thunks.

Affected modules: ITKCommon (3), ITKIOImageBase (3), ITKFEM (1), ITKOptimizers (11), ITKStatistics (8), ITKWatersheds (2), ITKVideoCore (1).

See: #6000

This is a backport to @hjmjohnson 's patch to ITK 5.

[greptile-apps]

Greptile Summary

This PR moves 30 exported non-template class destructors from inline = default in headers to out-of-line = default in their corresponding .cxx files, fixing hidden D1Ev/D0Ev destructor thunks under -fvisibility-inlines-hidden that break dynamic_cast across DSO boundaries in shared-library builds. The change is a mechanical, consistent backport of the fix from the main branch to release-5.4, covering 7 modules (ITKCommon, ITKIOImageBase, ITKFEM, ITKOptimizers, ITKStatistics, ITKWatersheds, ITKVideoCore).

The PR description states "ITKOptimizers (11)" but the changeset includes 12 optimizer classes (itkVersorTransformOptimizer is the 12th). This is a documentation-only discrepancy with no code impact.

Confidence Score: 5/5

This PR is safe to merge — all 30 destructor moves are mechanically correct and consistently applied across all 60 changed files.

Every header/source pair follows the same correct pattern: declaration-only ~ClassName() override; in the header, out-of-line ClassName::~ClassName() = default; in the .cxx. No logic is changed, no API is broken, and the fix directly addresses the documented ABI issue with -fvisibility-inlines-hidden. The only finding is a minor off-by-one in the PR description ('11' optimizers vs. 12 actual), which has no code impact.

No files require special attention — all changes are uniform and correct.

Important Files Changed

Filename	Overview
Modules/Core/Common/include/itkEquivalencyTable.h	Removes inline = default destructor; now declares ~EquivalencyTable() override; only — correct pattern
Modules/Core/Common/src/itkEquivalencyTable.cxx	Adds out-of-line EquivalencyTable::~EquivalencyTable() = default; — anchors destructor thunks correctly
Modules/Core/Common/include/itkLoggerManager.h	Inline = default destructor removed; declaration-only ~LoggerManager() override; retained — correct
Modules/Core/Common/src/itkLoggerManager.cxx	Out-of-line destructor added at top of translation unit — correct placement
Modules/Numerics/Optimizers/include/itkOptimizer.h	Declaration-only destructor ~Optimizer() override; — correct, consistent with the rest of the PR
Modules/Numerics/Optimizers/src/itkOptimizer.cxx	Out-of-line Optimizer::~Optimizer() = default; added — correctly anchors vtable and destructor thunks
Modules/Numerics/FEM/include/itkFEMLightObject.h	Declaration-only destructor left in header — correct fix for DSO visibility
Modules/Numerics/FEM/src/itkFEMLightObject.cxx	Out-of-line FEMLightObject::~FEMLightObject() = default; added inside nested itk::fem namespace — correct
Modules/Numerics/Statistics/src/itkChiSquareDistribution.cxx	Out-of-line destructor placed correctly before the constructor definition — matches established pattern
Modules/Video/Core/src/itkTemporalProcessObject.cxx	Out-of-line TemporalProcessObject::~TemporalProcessObject() = default; added — correct
Modules/Segmentation/Watersheds/src/itkOneWayEquivalencyTable.cxx	Out-of-line destructor definition added at top of namespace block — correct and consistent

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["Class declared with ITK*_EXPORT macro\n(shared library build)"]
    A --> B{Destructor placement?}
    B -- "Before (inline = default in header)" --> C["Compiled into every TU that includes header\nfvisibility-inlines-hidden hides D1Ev/D0Ev thunks\nBreaks dynamic_cast across DSO boundaries"]
    B -- "After (out-of-line = default in .cxx)" --> D["Compiled into exactly one TU\nDestructor has default (exported) visibility\nAll destructor thunks anchored and exported"]
    C --> E["❌ dynamic_cast fails across DSO boundaries\n(shared library builds)"]
    D --> F["✅ dynamic_cast works correctly\nacross DSO boundaries"]

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[hjmjohnson]

Thanks Matt!