Add readonly to structs

OpenRA.Game/Map/Map.cs

@@ -24,7 +24,7 @@ using OpenRA.Traits;
 
 namespace OpenRA
 {
-	struct BinaryDataHeader
+	readonly struct BinaryDataHeader
 	{
 		public readonly byte Format;
 		public readonly uint TilesOffset;
@@ -1225,7 +1225,7 @@ namespace OpenRA
 			return AllEdgeCells.Random(rand);
 		}
 
-		public WDist DistanceToEdge(WPos pos, WVec dir)
+		public WDist DistanceToEdge(WPos pos, in WVec dir)
 		{
 			var projectedPos = pos - new WVec(0, pos.Z, pos.Z);
 			var x = dir.X == 0 ? int.MaxValue : ((dir.X < 0 ? ProjectedTopLeft.X : ProjectedBottomRight.X) - projectedPos.X) / dir.X;

OpenRA.Game/Map/MapCoordsRegion.cs

@@ -14,7 +14,7 @@ using System.Collections.Generic;
 
 namespace OpenRA
 {
-	public struct MapCoordsRegion : IEnumerable<MPos>
+	public readonly struct MapCoordsRegion : IEnumerable<MPos>
 	{
 		public struct MapCoordsEnumerator : IEnumerator<MPos>
 		{

OpenRA.Game/Map/MapGrid.cs

@@ -22,7 +22,7 @@ namespace OpenRA
 	public enum RampSplit { Flat, X, Y }
 	public enum RampCornerHeight { Low = 0, Half = 1, Full = 2 }
 
-	public struct CellRamp
+	public readonly struct CellRamp
 	{
 		public readonly int CenterHeightOffset;
 		public readonly WVec[] Corners;

OpenRA.Game/Map/TileReference.cs

@@ -11,7 +11,7 @@
 
 namespace OpenRA
 {
-	public struct TerrainTile
+	public readonly struct TerrainTile
 	{
 		public readonly ushort Type;
 		public readonly byte Index;
@@ -27,7 +27,7 @@ namespace OpenRA
 		public override string ToString() { return Type + "," + Index; }
 	}
 
-	public struct ResourceTile
+	public readonly struct ResourceTile
 	{
 		public readonly byte Type;
 		public readonly byte Index;