Optimize contains() on large arrays

src/main/java/com/schibsted/spt/data/jslt/impl/AbstractFunction.java

@@ -0,0 +1,25 @@
+
+// Copyright 2018 Schibsted Marketplaces Products & Technology As
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.schibsted.spt.data.jslt.impl;
+
+import com.schibsted.spt.data.jslt.Function;
+
+public abstract class AbstractFunction extends AbstractCallable implements Function {
+
+  public AbstractFunction(String name, int min, int max) {
+    super(name, min, max);
+  }
+}

src/main/java/com/schibsted/spt/data/jslt/impl/BuiltinFunctions.java

@@ -117,13 +117,6 @@ public class BuiltinFunctions {
     macros.put("fallback", new BuiltinFunctions.Fallback());
   }
 
-  private static abstract class AbstractFunction extends AbstractCallable implements Function {
-
-    public AbstractFunction(String name, int min, int max) {
-      super(name, min, max);
-    }
-  }
-
   private static abstract class AbstractMacro extends AbstractCallable implements Macro {
 
     public AbstractMacro(String name, int min, int max) {

src/main/java/com/schibsted/spt/data/jslt/impl/FunctionExpression.java

@@ -55,4 +55,25 @@ public JsonNode apply(Scope scope, JsonNode input) {
     else
       return function.call(input, params);
   }
+
+  private static final int OPTIMIZE_ARRAY_CONTAINS_MIN = 10;
+  public ExpressionNode optimize() {
+    super.optimize();
+
+    // if the second argument to contains() is an array with a large
+    // number of elements, don't do a linear search. instead, use an
+    // optimized version of the function that uses a HashSet
+    if (function == BuiltinFunctions.functions.get("contains") &&
+        arguments.length == 2 &&
+        (arguments[1] instanceof LiteralExpression)) {
+
+      JsonNode v = arguments[1].apply(null, null);
+      if (v.isArray() && v.size() > OPTIMIZE_ARRAY_CONTAINS_MIN) {
+        // we use resolve to make sure all references are updated
+        resolve(new OptimizedStaticContainsFunction(v));
+      }
+    }
+
+    return this;
+  }
 }

src/main/java/com/schibsted/spt/data/jslt/impl/OptimizedStaticContainsFunction.java

@@ -0,0 +1,45 @@
+
+// Copyright 2019 Schibsted Marketplaces Products & Technology As
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.schibsted.spt.data.jslt.impl;
+
+import java.util.Set;
+import java.util.HashSet;
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.node.BooleanNode;
+
+/**
+ * An optimized version of contains(a, b) which is used when b is an
+ * array literal with a large number of values, so that a linear
+ * search becomes a performance drag.
+ */
+public class OptimizedStaticContainsFunction extends AbstractFunction {
+  private Set<JsonNode> values;
+
+  public OptimizedStaticContainsFunction(JsonNode array) {
+    super("optimized-static-contains", 2, 2);
+
+    this.values = new HashSet();
+    for (int ix = 0; ix < array.size(); ix++)
+      values.add(array.get(ix));
+  }
+
+  public JsonNode call(JsonNode input, JsonNode[] arguments) {
+    if (values.contains(arguments[0]))
+      return BooleanNode.TRUE;
+    else
+      return BooleanNode.FALSE;
+  }
+}