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C# Local Function

Summary

C# local functions can be used in a method locally to repeat operations. It can access all variables defined in the parent method.

Overview

C# local functions can be defined using this syntax:

Func <T..., TResult> FuncName = (T t, ...) =>
{
   ...
   return TResult;
}

Local function has the same scope as the parent method. It can therefore access all local variable, class members and arguments. Local functions can be used to repeat operations that is only used within the parent method.

An example

public Point3D[] GetExtents(Rect[] rects, Circle[] circs)
{
   double xmin, xmax, ymin, ymax;
   xmin = ymin = double.MaxValue;
   xmax = ymax = double.MinValue;

   Func<double, double, bool> UpdateExtent = (double x, double y) =>
   {
      if (x < xmin) xmin = x;
      if (x > xmax) xmax = x;
      if (y < ymin) ymin = y;
      if (y > ymax) ymax = y;
      return true;
   };

   // Do rectangles
   foreach (var rect in rects)
   {
      UpdateExtent(rect.Left, rect.Bottom);
      UpdateExtent(rect.Top, rect.Right);
   }

   // Do circles
   foreach (var c in circs)
   {
      UpdateExtent(c.Center.X - c.Radius, c.Center.Y - c.Radius);
      UpdateExtent(c.Center.X + c.Radius, c.Center.Y + c.Radius);
   }
   return new Point3D[] { new Point3D(xmin, ymin, 0), 
       new Point3D(xmax, ymax, 0) };
}