Make line a let constant.

Author: scottrhoyt

Sources/GeographicLib/GeodesicLine.swift

@@ -13,7 +13,7 @@ import CGeographicLib
 /// This struct represents a geodesic starting at a given point with a given azimuth.
 /// It allows for efficient computation of points along the geodesic.
 public struct GeodesicLine: Sendable {
-    internal var line: geod_geodesicline
+    internal let line: geod_geodesicline
 
     // MARK: - Properties
 
@@ -59,10 +59,15 @@ public struct GeodesicLine: Sendable {
     ///   - capabilities: Capabilities for calculations (default: standard)
     public init(geodesic: Geodesic, latitude: Double, longitude: Double, azimuth: Double,
                 capabilities: GeodesicCapability = .standard) {
-        self.line = geod_geodesicline()
+        var line = geod_geodesicline()
         withUnsafePointer(to: geodesic.geod) { geodPtr in
-            geod_lineinit(&self.line, geodPtr, latitude, longitude, azimuth, capabilities.rawValue)
+            geod_lineinit(&line, geodPtr, latitude, longitude, azimuth, capabilities.rawValue)
         }
+        self.init(line: line)
+    }
+    
+    internal init(line: geod_geodesicline) {
+        self.line = line
     }
 
     // MARK: - Position Methods
@@ -193,10 +198,7 @@ public extension Geodesic {
             geod_directline(&line, geodPtr, latitude, longitude, azimuth, distance, capabilities.rawValue)
         }
 
-        var result = GeodesicLine(geodesic: self, latitude: latitude, longitude: longitude,
-                                azimuth: azimuth, capabilities: capabilities)
-        result.line = line
-        return result
+        return GeodesicLine(line: line)
     }
 
     /// Create a geodesic line from an inverse problem.
@@ -220,10 +222,7 @@ public extension Geodesic {
             geod_inverseline(&line, geodPtr, startLatitude, startLongitude, endLatitude, endLongitude, capabilities.rawValue)
         }
 
-        var result = GeodesicLine(geodesic: self, latitude: startLatitude, longitude: startLongitude,
-                                azimuth: 0, capabilities: capabilities)
-        result.line = line
-        return result
+        return GeodesicLine(line: line)
     }
 }