Context builder fix

README.md

@@ -71,6 +71,8 @@ opel supports:
 - registrable functions (i.e. `myFunction('Hello, World!')`)
 - registrable constant values (i.e. `'Hello, ' + WORLD_VALUE`)
 
+More can be found in [documentation](https://github.com/allegro/opel/wiki).
+
 ## Using with Gradle
 
 Basically, all you have to do is to add a compile dependency:

src/main/java/pl/allegro/tech/opel/EvalContextBuilder.java

@@ -11,15 +11,17 @@ public class EvalContextBuilder {
     private Optional<EvalContext> externalEvalContext = Optional.empty();
 
     static EvalContext fromMaps(Map<String, CompletableFuture<Object>> values, Map<String, OpelAsyncFunction<?>> functions) {
+        Map<String, CompletableFuture<Object>> copiedValues = new HashMap<>(values);
+        Map<String, OpelAsyncFunction<?>> copiedFunctions = new HashMap<>(functions);
         return new EvalContext() {
             @Override
             public Optional<OpelAsyncFunction<?>> getFunction(String name) {
-                return Optional.ofNullable(functions.get(name));
+                return Optional.ofNullable(copiedFunctions.get(name));
             }
 
             @Override
             public Optional<CompletableFuture<?>> getValue(String name) {
-                return Optional.ofNullable(values.get(name));
+                return Optional.ofNullable(copiedValues.get(name));
             }
         };
     }

src/test/groovy/pl/allegro/tech/opel/EvalContextBuilderSpec.groovy

@@ -43,4 +43,21 @@ class EvalContextBuilderSpec extends Specification {
         context.getValue('v').get().get() == 'value1'
         context.getFunction('f').get().apply([]).get() == 'from fun 1'
     }
+
+    def "adding new values should not change built context"() {
+        given:
+        def builder = create()
+            .withCompletedValue('a', 'a')
+        def context1 = builder.build()
+
+        when:
+        builder.withCompletedValue('b', 'b')
+        def context2 = builder.build()
+
+        then:
+        context1.getValue('a').isPresent()
+        !context1.getValue('b').isPresent()
+        context2.getValue('a').isPresent()
+        context2.getValue('b').isPresent()
+    }
 }