Background and motivation

Most applications performing 2D and 3D spatial calculations need to convert between radians and degrees. For example, Unity includes the constants Mathf.Deg2Rad and Rad2Deg; Microsoft XNA/MonoGame includes the functions MathHelper.ToDegrees and ToRadians; and NetTopologySuite inclues the methods Radians.ToDegrees and Degrees.ToRadians.

API Proposal

  namespace System.Numerics {
      public interface ITrigonometricFunctions<TSelf> {
+         public static abstract TSelf ToDegrees(TSelf radians);
+         public static abstract TSelf ToRadians(TSelf degrees);
      }
  }

And, if Math and MathF can still evolve despite the introduction of generic math, it would be nice to also include sugar for these there.

namespace System
{
    public static class Math
    {
+        public static double ToDegrees(double radians) => radians.ToDegrees();
+        public static double ToRadians(double degrees) => degrees.ToDegrees();
    }
    public static class MathF
    {
+        public static float ToDegrees(float radians) => radians.ToDegrees();
+        public static float ToRadians(float degrees) => degrees.ToDegrees();
    }
}

API Usage

var angleInRadians = Math.PI;

// Convert from radians to degrees. Returns 180.0
var angleInDegrees= double.ToDegrees(angleInRadians);

// Convert from degrees to radians. Returns (an aproximation of) π
angleInRadians= double.ToRadians(angleInDegrees);

Alternative Designs

An alternative design was proposed in #38566:

  namespace System {
      public static class MathF {
+        public const float RadiansToDegrees = 57.295779513f;
+        public const float DegreesToRadians = 0.0174532925f;
    }

However, this was rejected in favor of methods:

Functions will allow a more precise implementation to be provided or for other optimizations to occur, without restricting things.

There was one counterpoint that should still be considered tough:

A constant could also be used for vectors

var input = new Vector3(10f, 20f, 30f) * MathF.DegreesToRadians;

Risks

• Adding members to an interface is always risky
• There may be some churn and confusion as developers migrate from various APIs in existing libraries, but this is short-term