STYLE: Replace declare-then-Fill(N) with ::Filled(N) factory method

[hjmjohnson]

Summary

Replaces the verbose two-line FixedArray initialization pattern with the modern single-line static factory method ::Filled(v).

Before:

ImageType::SizeType size;
size.Fill(16);

After:

constexpr auto size = ImageType::SizeType::Filled(16);

Rules applied

• constexpr auto used when the variable is never subsequently modified (test files with concrete types)
• auto (without constexpr) used for accumulator variables in loop bodies (.hxx template implementations)
• Skipped: cases where Fill() is immediately followed by element-wise overrides (size[0] = w), or where typename disambiguation in deeply nested template parameter scopes makes the replacement non-trivial

Files changed

File	Pattern
Modules/IO/NRRD/test/itkNrrdLocaleTest.cxx	SizeType + IndexType → constexpr auto
Modules/Video/BridgeOpenCV/test/itkOpenCVVideoIOTest.cxx	PointType → constexpr auto
Modules/Filtering/Path/include/itkChainCodeToFourierSeriesPathFilter.hxx	VectorType accumulators → auto
Modules/Filtering/QuadEdgeMeshFiltering/include/itkSmoothingQuadEdgeMeshFilter.hxx	VectorType accumulator → auto

Pure style change — no semantic changes.

Suggested by @N-Dekker in #6003 (comment)

[greptile-apps]

Greptile Summary

This PR applies a consistent style modernization across 52 files, replacing the two-line T var; var.Fill(N) initialization pattern with either auto var = itk::MakeFilled<T>(N) for non-zero fills or T var{} for zero fills. All replacements are semantically equivalent — itk::MakeFilled is the correct ITK factory for non-zero construction, and {} value-initialization of FixedArray correctly zeroes its underlying C-array data member because FixedArray's default constructor is = default, causing value-init to zero every element.

Confidence Score: 5/5

Pure style change — all replacements are semantically equivalent and safe to merge

All 52 files apply only mechanical, semantics-preserving substitutions. {} on FixedArray correctly zero-initializes via value-init of its C-array member, and itk::MakeFilled is the intended ITK API for filled construction. No logic paths, data flows, or interfaces are altered.

No files require special attention

Important Files Changed

Filename	Overview
Modules/Core/ImageFunction/include/itkGaussianInterpolateImageFunction.hxx	Replaces three Fill(0.0) calls with {} value-initialization on FixedArray accumulators — semantically equivalent since FixedArray's defaulted constructor value-initializes its C-array to zero
Modules/Registration/Common/include/itkLandmarkBasedTransformInitializer.hxx	Replaces Fill(0.0) with {} on VectorType accumulators at three sites — correct zero-initialization
Modules/Filtering/Path/include/itkFourierSeriesPath.hxx	Replaces output.Fill(0) with output{} in Evaluate and EvaluateDerivative — correct zero-initialization of path outputs
Modules/Filtering/Path/include/itkChainCodeToFourierSeriesPathFilter.hxx	Replaces Fill(0.0) with {} on cosCoefficient/sinCoefficient VectorType accumulators inside the harmonic loop
Modules/Filtering/QuadEdgeMeshFiltering/include/itkSmoothingQuadEdgeMeshFilter.hxx	Replaces Fill(0) with {} on VectorType accumulator in GenerateData
Modules/Segmentation/KLMRegionGrowing/include/itkKLMRegionGrowImageFilter.hxx	Replaces Fill(0) with {} on index accumulators inside InitializeKLM loop — correct zero-initialization
Modules/Video/Core/include/itkVideoStream.h	Replaces start.Fill(0) with start{} in header example code
Modules/Core/Common/test/itkBSplineInterpolationWeightFunctionTest.cxx	Replaces ContinuousIndexType declare+Fill(4.15) with itk::MakeFilled
Modules/Filtering/ImageGrid/test/itkBSplineControlPointImageFunctionTest.cxx	Mixed: size/spacing use MakeFilled, index/origin use {}; subsequent .Fill() calls on the same mutable auto variables at lines 53-65 remain valid
Modules/Filtering/ImageGrid/test/itkBSplineScatteredDataPointSetToImageFilterTest3.cxx	Consolidates size declaration to itk::MakeFilled with the computed value inline
Modules/Registration/RegistrationMethodsv4/test/itkTimeVaryingBSplineVelocityFieldPointSetRegistrationTest.cxx	Replaces multiple declare+Fill patterns for domain/velocity field parameters with MakeFilled and {} initialization
Modules/Registration/Common/test/itkMultiResolutionPyramidImageFilterTest.cxx	Replaces Vector declare+Fill with itk::MakeFilled using the computed shift value inline

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["T var (uninitialized)"] --> B["var.Fill(N) — explicit init"]
    C["auto var = itk::MakeFilled<T>(N)"] --> D["var initialized to N at construction"]
    E["T var{}"] --> F["var zero-initialized at construction"]
    A -. "replaced by (non-zero N)" .-> C
    A -. "replaced by (zero N)" .-> E
    B -. removed .-> C
    B -. removed .-> E
    style A fill:#f9f,stroke:#333
    style B fill:#f9f,stroke:#333
    style C fill:#9f9,stroke:#333
    style D fill:#9f9,stroke:#333
    style E fill:#9f9,stroke:#333
    style F fill:#9f9,stroke:#333

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_{Reviews (2): Last reviewed commit: "STYLE: Use {}-initialization for zero-fi..." | Re-trigger Greptile}

[dzenanz]

Possibly squash commits. Good even as-is.

[hjmjohnson]

Thanks @dzenanz I am doing a more complete review and making a more extensive addresing of this style of fix. I'm moving it to a draft until I determine if the a more complete solution can be found.

[hjmjohnson]

ARMBUILD-Python failure analysis

The ARMBUILD-Python failure in run 23983133045 is not caused by this PR and is not a disk space issue.

Root cause: clang++: error: unable to execute command: Abort trap: 6 — a SIGABRT during SWIG Python wrapper compilation on the macos-15-arm64 runner.

Evidence:

• The crash occurred during the build phase, not testing — 2623 of 2860 tests were "Not Run"
• This PR only modifies C++ .hxx headers and test .cxx files — no Python wrapping code is touched
• The same ARMBUILD-Python job passes on main (commit b94cca5)
• Abort trap: 6 on macOS clang during SWIG compilation is characteristic of an out-of-memory condition — the macos-15-arm64 GitHub runner has 7 GB RAM, and SWIG-generated translation units can exceed this during compilation

Likely cause: Transient OOM on the ARM64 runner due to concurrent memory pressure. A re-run should resolve it.