Make Source a sealed interface

3 files changed, 3 insertions, 3 deletions

diff --git a/src/main/java/org/shedlang/compiler/sources/NullSource.java b/src/main/java/org/shedlang/compiler/sources/NullSource.java
index 6a66aeea..fbac0ea0 100644
--- a/src/main/java/org/shedlang/compiler/sources/NullSource.java
+++ b/src/main/java/org/shedlang/compiler/sources/NullSource.java
@@ -1,6 +1,6 @@
 package org.shedlang.compiler.sources;
 
-public class NullSource implements Source {
+public final class NullSource implements Source {
     private NullSource() {
     }
 
diff --git a/src/main/java/org/shedlang/compiler/sources/RuntimeSource.java b/src/main/java/org/shedlang/compiler/sources/RuntimeSource.java
index 6bb708f9..749b84e3 100644
--- a/src/main/java/org/shedlang/compiler/sources/RuntimeSource.java
+++ b/src/main/java/org/shedlang/compiler/sources/RuntimeSource.java
@@ -1,6 +1,6 @@
 package org.shedlang.compiler.sources;
 
-public class RuntimeSource implements Source {
+public final class RuntimeSource implements Source {
     private RuntimeSource() {
     }
 
diff --git a/src/main/java/org/shedlang/compiler/sources/Source.java b/src/main/java/org/shedlang/compiler/sources/Source.java
index edd9ad88..aeae447f 100644
--- a/src/main/java/org/shedlang/compiler/sources/Source.java
+++ b/src/main/java/org/shedlang/compiler/sources/Source.java
@@ -1,5 +1,5 @@
 package org.shedlang.compiler.sources;
 
-public interface Source {
+public sealed interface Source permits FileFragmentSource, NullSource, RuntimeSource {
     String describe();
 }