src/java.base/share/classes/java/lang/invoke/MethodHandles.java

rev 15544 : imported patch fold_select

@@ -3941,10 +3941,37 @@
         if (!ok)
             throw misMatchedTypes("target and combiner types", targetType, combinerType);
         return rtype;
     }
 
+    private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType, int ... argPos) {
+        int foldArgs = combinerType.parameterCount();
+        if (argPos.length != foldArgs) {
+            throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
+        }
+        Class<?> rtype = combinerType.returnType();
+        int foldVals = rtype == void.class ? 0 : 1;
+        boolean ok = true;
+        for (int i = 0; i < foldArgs; i++) {
+            int arg = argPos[i];
+            if (arg < 0 || arg > targetType.parameterCount()) {
+                throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
+            }
+            if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
+                throw newIllegalArgumentException("target argument type at position " + arg 
+                        + " must match combiner argument type at index " + i + ": " + targetType
+                        + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
+            }
+        }
+        if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos)) {
+            ok = false;
+        }
+        if (!ok)
+            throw misMatchedTypes("target and combiner types", targetType, combinerType);
+        return rtype;
+    }
+
     /**
      * Makes a method handle which adapts a target method handle,
      * by guarding it with a test, a boolean-valued method handle.
      * If the guard fails, a fallback handle is called instead.
      * All three method handles must have the same corresponding

@@ -4947,10 +4974,32 @@
         }
         result = result.copyWithExtendL(newType, lform, combiner);
         return result;
     }
 
+    /** 
+     * 
+     * @param target
+     * @param pos
+     * @param combiner
+     * @param argPositions
+     * @return 
+     */
+    static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner, int ... argPositions) {
+        MethodType targetType = target.type();
+        MethodType combinerType = combiner.type();
+        Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType, argPositions);
+        BoundMethodHandle result = target.rebind();
+        boolean dropResult = rtype == void.class;
+        LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType(), argPositions);
+        MethodType newType = targetType;
+        if (!dropResult) {
+            newType = newType.dropParameterTypes(pos, pos + 1);
+        }
+        result = result.copyWithExtendL(newType, lform, combiner);
+        return result;
+    }
 
     private static void checkLoop0(MethodHandle[][] clauses) {
         if (clauses == null || clauses.length == 0) {
             throw newIllegalArgumentException("null or no clauses passed");
         }