Seal FileSystem interface

Author: fzhinkin

core/common/src/files/FileSystem.kt

@@ -14,7 +14,7 @@ import kotlinx.io.Source
  *
  * **This API is unstable and subject to change.**
  */
-public interface FileSystem {
+public sealed interface FileSystem {
     /**
      * Path to a directory suitable for creating temporary files.
      */
@@ -88,7 +88,7 @@ public interface FileSystem {
      * @throws kotlinx.io.files.FileNotFoundException when the file does not exist.
      * @throws kotlinx.io.IOException when it's not possible to open the file for reading.
      */
-    public fun read(path: Path): Source = path.source()
+    public fun read(path: Path): Source
 
     /**
      * Returns [Sink] to write into a file represented by the [path].
@@ -100,7 +100,7 @@ public interface FileSystem {
      *
      * @throws kotlinx.io.IOException when it's not possible to open the file for writing.
      */
-    public fun write(path: Path): Sink = path.sink()
+    public fun write(path: Path): Sink
 
     /**
      * Return [FileMetadata] associated with a file or directory represented by the [path].
@@ -119,11 +119,17 @@ public interface FileSystem {
     }
 }
 
+internal abstract class SystemFileSystemImpl : FileSystem {
+    override fun read(path: Path): Source = path.source()
+
+    override fun write(path: Path): Sink = path.sink()
+}
+
 internal expect val SystemFileSystem: FileSystem
 
 public class FileMetadata(
     public val isRegularFile: Boolean = false,
     public val isDirectory: Boolean = false
 )
 
-public expect open class FileNotFoundException(message: String?) : IOException
+public expect class FileNotFoundException(message: String?) : IOException

core/js/src/files/FileSystemJs.kt

@@ -25,7 +25,11 @@ internal val os: dynamic
         }
     }
 
-internal actual val SystemFileSystem: FileSystem = object : FileSystem {
+private class JsFileSystem : SystemFileSystemImpl() {
+    companion object {
+        val Instance = JsFileSystem()
+    }
+
     override val temporaryDirectory: Path
         get() {
             check(os !== null) { "Module 'os' was not found" }
@@ -104,6 +108,8 @@ internal actual val SystemFileSystem: FileSystem = object : FileSystem {
     }
 }
 
+internal actual val SystemFileSystem: FileSystem = JsFileSystem.Instance
+
 public actual open class FileNotFoundException actual constructor(
     message: String?,
 ) : IOException(message)

core/jvm/src/files/FileSystemJvm.kt

@@ -41,7 +41,7 @@ private val mover: Mover by lazy {
     }
 }
 
-private class JvmFileSystem : FileSystem {
+private class JvmFileSystem : SystemFileSystemImpl() {
     companion object {
         val Instance = JvmFileSystem()
     }

core/native/src/files/FileSystemNative.kt

@@ -11,7 +11,7 @@ import platform.posix.*
 
 internal expect val NativeTempDir: Path
 
-private class NativeFileSystem : FileSystem {
+private class NativeFileSystem : SystemFileSystemImpl() {
     companion object {
         val Instance = NativeFileSystem()
     }
@@ -85,7 +85,7 @@ internal expect fun atomicMoveImpl(source: Path, destination: Path)
 
 internal expect fun mkdirImpl(path: String)
 
-public actual val SystemFileSystem: FileSystem
+internal actual val SystemFileSystem: FileSystem
     get() = NativeFileSystem.Instance
 
 public actual open class FileNotFoundException actual constructor(