diff --git a/src/17.cs b/src/17.cs
index 64b18d6..d983d08 100644
--- a/src/17.cs
+++ b/src/17.cs
@@ -113,21 +113,21 @@ internal class Day17 : Day
                 {
                     if (canMove(rockIdx, rockPos, grid, ivec2.RIGHT))
                     {
-                        rockPos.x++;
+                        rockPos = new ivec2(rockPos.x + 1, rockPos.y);
                     }
                 }
                 else
                 {
                     if (canMove(rockIdx, rockPos, grid, ivec2.LEFT))
                     {
-                        rockPos.x--;
+                        rockPos = new ivec2(rockPos.x - 1, rockPos.y);
                     }
                 }
 
                 // inverted up/down for this...
                 if (canMove(rockIdx, rockPos, grid, ivec2.UP))
                 {
-                    rockPos.y--;
+                    rockPos = new ivec2(rockPos.x, rockPos.y - 1);
                 }
                 else
                 {
@@ -174,21 +174,21 @@ internal class Day17 : Day
                 {
                     if (canMove(rockIdx, rockPos, grid, ivec2.RIGHT))
                     {
-                        rockPos.x++;
+                        rockPos = new ivec2(rockPos.x + 1, rockPos.y);
                     }
                 }
                 else
                 {
                     if (canMove(rockIdx, rockPos, grid, ivec2.LEFT))
                     {
-                        rockPos.x--;
+                        rockPos = new ivec2(rockPos.x - 1, rockPos.y);
                     }
                 }
 
                 // inverted up/down for this...
                 if (canMove(rockIdx, rockPos, grid, ivec2.UP))
                 {
-                    rockPos.y--;
+                    rockPos = new ivec2(rockPos.x, rockPos.y - 1);
                 }
                 else
                 {
diff --git a/src/22.cs b/src/22.cs
index f8c537c..f08407c 100644
--- a/src/22.cs
+++ b/src/22.cs
@@ -536,11 +536,11 @@ internal class Day22 : Day
             {
                 if (inst.turn == 'R')
                 {
-                    facing.RotateRight();
+                    facing = facing.GetRotatedRight();
                 }
                 else if (inst.turn == 'L')
                 {
-                    facing.RotateLeft();
+                    facing = facing.GetRotatedLeft();
                 }
             }
         }
@@ -591,11 +591,11 @@ internal class Day22 : Day
             {
                 if (inst.turn == 'R')
                 {
-                    facing.RotateRight();
+                    facing = facing.GetRotatedRight();
                 }
                 else if (inst.turn == 'L')
                 {
-                    facing.RotateLeft();
+                    facing = facing.GetRotatedLeft();
                 }
             }
         }
diff --git a/src/Util/Vec2.cs b/src/Util/Vec2.cs
index 83fc11d..f4e1654 100644
--- a/src/Util/Vec2.cs
+++ b/src/Util/Vec2.cs
@@ -1,9 +1,9 @@
 namespace aoc2022.Util;
 
-public struct ivec2 : IEquatable<ivec2>, IComparable<ivec2>, IComparable
+public readonly struct ivec2 : IEquatable<ivec2>, IComparable<ivec2>, IComparable
 {
-    public long x = 0;
-    public long y = 0;
+    public readonly long x = 0;
+    public readonly long y = 0;
 
     public static readonly ivec2 ZERO = new ivec2(0, 0);
     public static readonly ivec2 ONE = new ivec2(1, 1);
@@ -27,10 +27,8 @@ public struct ivec2 : IEquatable<ivec2>, IComparable<ivec2>, IComparable
     public long MaxElement => System.Math.Max(x, y);
 
     public ivec2 GetRotatedLeft() => new ivec2(y, -x);
-    public void RotateLeft() => this = GetRotatedLeft();
 
     public ivec2 GetRotatedRight() => new ivec2(-y, x);
-    public void RotateRight() => this = GetRotatedRight();
 
     public long Dot(ivec2 v) => (x * v.x) + (y * v.y);
     public long LengthSquared => (x * x) + (y * y);
diff --git a/src/Util/Vec3.cs b/src/Util/Vec3.cs
index 7e1eabc..9cc38c4 100644
--- a/src/Util/Vec3.cs
+++ b/src/Util/Vec3.cs
@@ -1,10 +1,10 @@
 namespace aoc2022.Util;
 
-public struct ivec3 : IEquatable<ivec3>, IComparable<ivec3>, IComparable
+public readonly struct ivec3 : IEquatable<ivec3>, IComparable<ivec3>, IComparable
 {
-    public long x = 0;
-    public long y = 0;
-    public long z = 0;
+    public readonly long x = 0;
+    public readonly long y = 0;
+    public readonly long z = 0;
 
     public static readonly ivec3 ZERO = new ivec3(0, 0, 0);
     public static readonly ivec3 ONE = new ivec3(1, 1, 1);
@@ -31,10 +31,8 @@ public struct ivec3 : IEquatable<ivec3>, IComparable<ivec3>, IComparable
     public long MinElement => System.Math.Min(x, System.Math.Min(y, z));
 
     public ivec3 GetRotatedLeft() => new ivec3(y, -x, z);
-    public void RotateLeft() => this = GetRotatedLeft();
 
     public ivec3 GetRotatedRight() => new ivec3(-y, x, z);
-    public void RotateRight() => this = GetRotatedRight();
 
     public long Dot(ivec3 v) => (x * v.x) + (y * v.y) + (z * v.z);
     public long LengthSquared => (x * x) + (y * y) +  (z * z);