Adding ObjectProvenance.maybeExtractProvenance to aid with evolving provenance classes. Refactored the tests to test both the new method and ObjectProvenance.checkAndExtractProvenance.

Author: Craigacp

olcut-core/src/main/java/com/oracle/labs/mlrg/olcut/provenance/ObjectProvenance.java

@@ -32,6 +32,7 @@
 import com.oracle.labs.mlrg.olcut.util.Pair;
 
 import java.util.Map;
+import java.util.Optional;
 
 /**
  * A provenance object which records object fields.
@@ -83,7 +84,7 @@ default public String generateString(String name) {
     /**
      * Removes the specified Provenance from the supplied map and returns it. Checks that it's the right type,
      * and casts to it before returning.
-     *
+     * <p>
      * Throws ProvenanceException if it's not found or it's an incorrect type.
      * @param map The map to check.
      * @param key The key to look up.
@@ -95,15 +96,40 @@ default public String generateString(String name) {
      */
     @SuppressWarnings("unchecked") // Guarded by isInstance check
     public static <T extends Provenance> T checkAndExtractProvenance(Map<String,Provenance> map, String key, Class<T> type, String provClassName) throws ProvenanceException {
+        Optional<T> prov = maybeExtractProvenance(map,key,type,provClassName);
+        if (prov.isPresent()) {
+            return prov.get();
+        } else {
+            throw new ProvenanceException("Failed to find " + key + " when constructing " + provClassName);
+        }
+    }
+
+    /**
+     * Removes the specified Provenance from the supplied map and returns it. Checks that it's the right type,
+     * and casts to it before returning. Unlike {@link #checkAndExtractProvenance(Map, String, Class, String)} it doesn't
+     * throw if it fails to find the key, only if the value is of the wrong type.
+     * <p>
+     * This is used when evolving provenance classes by adding new fields to ensure that old serialized
+     * forms remain compatible.
+     * @param map The map to inspect.
+     * @param key The key to find.
+     * @param type The class of the value.
+     * @param provClassName The name of the requesting class (to ensure the exception has the appropriate error message).
+     * @param <T> The type of the value.
+     * @return An optional containing the value if present.
+     * @throws ProvenanceException If the value is the wrong type.
+     */
+    @SuppressWarnings("unchecked") // Guarded by isInstance check
+    public static <T extends Provenance> Optional<T> maybeExtractProvenance(Map<String,Provenance> map, String key, Class<T> type, String provClassName) throws ProvenanceException {
         Provenance tmp = map.remove(key);
         if (tmp != null) {
             if (type.isInstance(tmp)) {
-                return (T) tmp;
+                return Optional.of((T) tmp);
             } else {
                 throw new ProvenanceException("Failed to cast " + key + " when constructing " + provClassName + ", found " + tmp);
             }
         } else {
-            throw new ProvenanceException("Failed to find " + key + " when constructing " + provClassName);
+            return Optional.empty();
         }
     }
 }

olcut-core/src/test/java/com/oracle/labs/mlrg/olcut/provenance/ExampleProvenancableConfigurable.java

@@ -41,6 +41,9 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
+import java.util.Optional;
+
+import static org.junit.jupiter.api.Assertions.fail;
 
 /**
  * Test class for the provenance system.
@@ -122,17 +125,20 @@ public ExampleProvenance(ExampleProvenancableConfigurable host) {
 
         @SuppressWarnings("unchecked")
         public ExampleProvenance(Map<String,Provenance> provenances) {
+            this.className = ObjectProvenance.checkAndExtractProvenance(provenances,ObjectProvenance.CLASS_NAME,StringProvenance.class,ExampleProvenance.class.getName()).getValue();
+            this.map = ObjectProvenance.checkAndExtractProvenance(provenances,MAP,MapProvenance.class,ExampleProvenance.class.getName());
+            Optional<DoubleProvenance> opt = ObjectProvenance.maybeExtractProvenance(provenances,DOUBLE_FIELD,DoubleProvenance.class,ExampleProvenance.class.getName());
+            if (opt.isPresent()) {
+                this.doubleField = opt.get();
+            } else {
+                throw new ProvenanceException("Failed to find " + DOUBLE_FIELD + " when constructing ExampleProvenance");
+            }
+            Optional<DoubleProvenance> notPresentOpt = ObjectProvenance.maybeExtractProvenance(provenances,"DEFINITELY-NOT-HERE",DoubleProvenance.class,ExampleProvenance.class.getName());
+            if (notPresentOpt.isPresent()) {
+                fail("Found a provenance which wasn't there");
+            }
+
             try {
-                if (provenances.containsKey(ObjectProvenance.CLASS_NAME)) {
-                    this.className = provenances.get(ObjectProvenance.CLASS_NAME).toString();
-                } else {
-                    throw new ProvenanceException("Failed to find class name when constructing ExampleProvenance");
-                }
-                if (provenances.containsKey(DOUBLE_FIELD)) {
-                    this.doubleField = (DoubleProvenance) provenances.get(DOUBLE_FIELD);
-                } else {
-                    throw new ProvenanceException("Failed to find " + DOUBLE_FIELD + " when constructing ExampleProvenance");
-                }
                 if (provenances.containsKey(INT_ARRAY_FIELD)) {
                     this.intArrayField = (ListProvenance<IntProvenance>) provenances.get(INT_ARRAY_FIELD);
                 } else {
@@ -143,11 +149,6 @@ public ExampleProvenance(Map<String,Provenance> provenances) {
                 } else {
                     throw new ProvenanceException("Failed to find " + EXAMPLES + " when constructing ExampleProvenance");
                 }
-                if (provenances.containsKey(MAP)) {
-                    this.map = (MapProvenance<StringProvenance>) provenances.get(MAP);
-                } else {
-                    throw new ProvenanceException("Failed to find " + MAP + " when constructing ExampleProvenance");
-                }
             } catch (ClassCastException e) {
                 throw new ProvenanceException("Incorrect type found in provenance, did not match the field type.",e);
             }