STYLE: Reduce indentation else after return

    Reduce indentation where possible and where it makes understanding code easier.
    Early exit is one of the suggested enforcements of that. Please do not use else
    or else if after something that interrupts control flow - like return, break,
    continue, throw.

    clang-tidy readability-else-after-return

Examples/RegistrationITKv4/ImageRegistrationHistogramPlotter.cxx

@@ -147,10 +147,7 @@ class RescaleDynamicRangeFunctor
       {
         return static_cast<OutputPixelType>(255);
       }
-      else
-      {
-        return itk::Math::Round<OutputPixelType>(-(30.0 * std::log(A)));
-      }
+      return itk::Math::Round<OutputPixelType>(-(30.0 * std::log(A)));
     }
     else
     {

Examples/Statistics/WeightedSampleStatistics.cxx

@@ -84,10 +84,8 @@ class ExampleWeightFunction
     {
       return 0.5;
     }
-    else
-    {
-      return 0.01;
-    }
+
+    return 0.01;
   }
 
 protected:

Modules/Bridge/VTK/src/itkVTKImageExportBase.cxx

@@ -159,10 +159,8 @@ VTKImageExportBase::PipelineModifiedCallback()
     m_LastPipelineMTime = pipelineMTime;
     return 1;
   }
-  else
-  {
-    return 0;
-  }
+
+  return 0;
 }
 
 /**

Modules/Core/Common/include/itkBSplineDerivativeKernelFunction.h

@@ -109,7 +109,7 @@ class ITK_TEMPLATE_EXPORT BSplineDerivativeKernelFunction : public KernelFunctio
     {
       return TRealValueType{ 0.5 };
     }
-    else if ((u > TRealValueType{ -1.0 }) && (u < TRealValueType{ 0.0 }))
+    if ((u > TRealValueType{ -1.0 }) && (u < TRealValueType{ 0.0 }))
     {
       return TRealValueType{ 1.0 };
     }
@@ -139,7 +139,7 @@ class ITK_TEMPLATE_EXPORT BSplineDerivativeKernelFunction : public KernelFunctio
     {
       return (TRealValueType{ -2.0 } * u);
     }
-    else if ((u >= TRealValueType{ 0.5 }) && (u < TRealValueType{ 1.5 }))
+    if ((u >= TRealValueType{ 0.5 }) && (u < TRealValueType{ 1.5 }))
     {
       return (TRealValueType{ -1.5 } + u);
     }
@@ -161,7 +161,7 @@ class ITK_TEMPLATE_EXPORT BSplineDerivativeKernelFunction : public KernelFunctio
     {
       return (TRealValueType{ -2.0 } * u + TRealValueType{ 1.5 } * u * u);
     }
-    else if ((u > TRealValueType{ -1.0 }) && (u < TRealValueType{ 0.0 }))
+    if ((u > TRealValueType{ -1.0 }) && (u < TRealValueType{ 0.0 }))
     {
       return (TRealValueType{ -2.0 } * u - TRealValueType{ 1.5 } * u * u);
     }

Modules/Core/Common/include/itkBSplineKernelFunction.h

@@ -103,7 +103,7 @@ class ITK_TEMPLATE_EXPORT BSplineKernelFunction : public KernelFunctionBase<TRea
     {
       return TRealValueType{ 1.0 };
     }
-    else if (Math::ExactlyEquals(absValue, TRealValueType{ 0.5 }))
+    if (Math::ExactlyEquals(absValue, TRealValueType{ 0.5 }))
     {
       return TRealValueType{ 0.5 };
     }
@@ -122,10 +122,8 @@ class ITK_TEMPLATE_EXPORT BSplineKernelFunction : public KernelFunctionBase<TRea
     {
       return TRealValueType{ 1.0 } - absValue;
     }
-    else
-    {
-      return TRealValueType{ 0.0 };
-    }
+
+    return TRealValueType{ 0.0 };
   }
 
   /** Second order spline. */
@@ -138,7 +136,7 @@ class ITK_TEMPLATE_EXPORT BSplineKernelFunction : public KernelFunctionBase<TRea
       const TRealValueType sqrValue = itk::Math::sqr(absValue);
       return TRealValueType{ 0.75 } - sqrValue;
     }
-    else if (absValue < TRealValueType{ 1.5 })
+    if (absValue < TRealValueType{ 1.5 })
     {
       const TRealValueType sqrValue = itk::Math::sqr(absValue);
       // NOTE: 1.0/8.0 == 0.125
@@ -162,7 +160,7 @@ class ITK_TEMPLATE_EXPORT BSplineKernelFunction : public KernelFunctionBase<TRea
       return (TRealValueType{ 4.0 } - TRealValueType{ 6.0 } * sqrValue + TRealValueType{ 3.0 } * sqrValue * absValue) /
              TRealValueType{ 6.0 };
     }
-    else if (absValue < TRealValueType{ 2.0 })
+    if (absValue < TRealValueType{ 2.0 })
     {
       const TRealValueType sqrValue = itk::Math::sqr(absValue);
       return (TRealValueType{ 8.0 } - TRealValueType{ 12.0 } * absValue + TRealValueType{ 6.0 } * sqrValue -

Modules/Core/Common/include/itkColorTable.hxx

@@ -281,12 +281,10 @@ ColorTable<TComponent>::GetColor(unsigned int c)
   {
     return m_Color[c];
   }
-  else
-  {
-    RGBPixel<TComponent> pixel;
-    pixel.Set(0, 0, 0);
-    return pixel;
-  }
+
+  RGBPixel<TComponent> pixel;
+  pixel.Set(0, 0, 0);
+  return pixel;
 }
 
 template <typename TComponent>
@@ -329,10 +327,8 @@ ColorTable<TComponent>::GetColorName(unsigned int c)
   {
     return m_ColorName[c];
   }
-  else
-  {
-    return "";
-  }
+
+  return "";
 }
 
 template <typename TComponent>

Modules/Core/Common/include/itkConstNeighborhoodIterator.hxx

@@ -55,7 +55,7 @@ ConstNeighborhoodIterator<TImage, TBoundaryCondition>::IndexInBounds(const Neigh
   {
     return true;
   }
-  else if (this->InBounds()) // Is this whole neighborhood in bounds?
+  if (this->InBounds()) // Is this whole neighborhood in bounds?
   {
     return true;
   }
@@ -108,7 +108,7 @@ ConstNeighborhoodIterator<TImage, TBoundaryCondition>::IndexInBounds(const Neigh
   {
     return true;
   }
-  else if (this->InBounds()) // Is this whole neighborhood in bounds?
+  if (this->InBounds()) // Is this whole neighborhood in bounds?
   {
     return true;
   }
@@ -162,21 +162,19 @@ ConstNeighborhoodIterator<TImage, TBoundaryCondition>::GetPixel(NeighborIndexTyp
     IsInBounds = true;
     return (m_NeighborhoodAccessorFunctor.Get(this->operator[](n)));
   }
+
+  OffsetType offset;
+  OffsetType internalIndex;
+  const bool flag = this->IndexInBounds(n, internalIndex, offset);
+  if (flag)
+  {
+    IsInBounds = true;
+    return (m_NeighborhoodAccessorFunctor.Get(this->operator[](n)));
+  }
   else
   {
-    OffsetType offset;
-    OffsetType internalIndex;
-    const bool flag = this->IndexInBounds(n, internalIndex, offset);
-    if (flag)
-    {
-      IsInBounds = true;
-      return (m_NeighborhoodAccessorFunctor.Get(this->operator[](n)));
-    }
-    else
-    {
-      IsInBounds = false;
-      return (m_NeighborhoodAccessorFunctor.BoundaryCondition(internalIndex, offset, this, this->m_BoundaryCondition));
-    }
+    IsInBounds = false;
+    return (m_NeighborhoodAccessorFunctor.BoundaryCondition(internalIndex, offset, this, this->m_BoundaryCondition));
   }
 }
 

Modules/Core/Common/include/itkConstNeighborhoodIteratorWithOnlyIndex.hxx

@@ -57,7 +57,7 @@ ConstNeighborhoodIteratorWithOnlyIndex<TImage>::IndexInBounds(const NeighborInde
   {
     return true;
   }
-  else if (this->InBounds()) // Is this whole neighborhood in bounds?
+  if (this->InBounds()) // Is this whole neighborhood in bounds?
   {
     return true;
   }

Modules/Core/Common/include/itkConstShapedNeighborhoodIterator.h

@@ -179,10 +179,8 @@ class ITK_TEMPLATE_EXPORT ConstShapedNeighborhoodIterator : private Neighborhood
       {
         return true;
       }
-      else
-      {
-        return false;
-      }
+
+      return false;
     }
 
     void

Modules/Core/Common/include/itkConstShapedNeighborhoodIterator.hxx

@@ -92,18 +92,17 @@ ConstShapedNeighborhoodIterator<TImage, TBoundaryCondition>::DeactivateIndex(Nei
   {
     return;
   }
-  else
+
+  while (n != *it)
   {
-    while (n != *it)
+    ++it;
+    if (it == m_ActiveIndexList.end())
     {
-      ++it;
-      if (it == m_ActiveIndexList.end())
-      {
-        return;
-      }
+      return;
     }
-    m_ActiveIndexList.erase(it);
   }
+  m_ActiveIndexList.erase(it);
+
 
   // Did we just deactivate the index at the center of the neighborhood?
   if (n == this->GetCenterNeighborhoodIndex())

Modules/Core/Common/include/itkEquivalencyTable.h

@@ -98,10 +98,8 @@ class ITKCommon_EXPORT EquivalencyTable : public DataObject
     {
       return a;
     }
-    else
-    {
-      return result->second;
-    }
+
+    return result->second;
   }
 
   /** Lookup an equivalency in the table by recursing through all
@@ -120,10 +118,8 @@ class ITKCommon_EXPORT EquivalencyTable : public DataObject
     {
       return false;
     }
-    else
-    {
-      return true;
-    }
+
+    return true;
   }
 
   /** Erases the entry with key a.  */

Modules/Core/Common/include/itkFiniteCylinderSpatialFunction.hxx

@@ -106,10 +106,8 @@ FiniteCylinderSpatialFunction<VDimension, TInput>::Evaluate(const InputType & po
   {
     return 1;
   }
-  else
-  {
-    return 0;
-  }
+
+  return 0;
 }
 
 template <unsigned int VDimension, typename TInput>

Modules/Core/Common/include/itkFrustumSpatialFunction.hxx

@@ -77,7 +77,7 @@ FrustumSpatialFunction<VDimension, TInput>::Evaluate(const InputType & position)
 
     return 1;
   }
-  else if (m_RotationPlane == RotationPlaneEnum::RotateInYZPlane)
+  if (m_RotationPlane == RotationPlaneEnum::RotateInYZPlane)
   {
     const double dx = relativePosition[0];
     const double dy = relativePosition[1];

Modules/Core/Common/include/itkGaussianDerivativeOperator.hxx

@@ -219,10 +219,8 @@ GaussianDerivativeOperator<TPixel, VDimension, TAllocator>::ModifiedBesselI1(dou
   {
     return -accumulator;
   }
-  else
-  {
-    return accumulator;
-  }
+
+  return accumulator;
 }
 
 template <typename TPixel, unsigned int VDimension, typename TAllocator>
@@ -242,37 +240,35 @@ GaussianDerivativeOperator<TPixel, VDimension, TAllocator>::ModifiedBesselI(int
   {
     return 0.0;
   }
-  else
+
+  const double toy = 2.0 / itk::Math::abs(y);
+  double       qip = accumulator = 0.0;
+  double       qi = 1.0;
+  for (int j = 2 * (n + static_cast<int>(DIGITS * std::sqrt(static_cast<double>(n)))); j > 0; j--)
   {
-    const double toy = 2.0 / itk::Math::abs(y);
-    double       qip = accumulator = 0.0;
-    double       qi = 1.0;
-    for (int j = 2 * (n + static_cast<int>(DIGITS * std::sqrt(static_cast<double>(n)))); j > 0; j--)
+    const double qim = qip + j * toy * qi;
+    qip = qi;
+    qi = qim;
+    if (itk::Math::abs(qi) > 1.0e10)
     {
-      const double qim = qip + j * toy * qi;
-      qip = qi;
-      qi = qim;
-      if (itk::Math::abs(qi) > 1.0e10)
-      {
-        accumulator *= 1.0e-10;
-        qi *= 1.0e-10;
-        qip *= 1.0e-10;
-      }
-      if (j == n)
-      {
-        accumulator = qip;
-      }
+      accumulator *= 1.0e-10;
+      qi *= 1.0e-10;
+      qip *= 1.0e-10;
     }
-    accumulator *= ModifiedBesselI0(y) / qi;
-    if (y < 0.0 && (n & 1))
+    if (j == n)
     {
-      return -accumulator;
-    }
-    else
-    {
-      return accumulator;
+      accumulator = qip;
     }
   }
+  accumulator *= ModifiedBesselI0(y) / qi;
+  if (y < 0.0 && (n & 1))
+  {
+    return -accumulator;
+  }
+  else
+  {
+    return accumulator;
+  }
 }
 
 template <typename TPixel, unsigned int VDimension, typename TAllocator>