--- /dev/null	2019-12-04 18:44:18.020007537 +0000
+++ new/src/jdk.incubator.foreign/share/classes/jdk/incubator/foreign/GroupLayout.java	2019-12-09 18:15:27.187950412 +0000
@@ -0,0 +1,210 @@
+/*
+ *  Copyright (c) 2019, Oracle and/or its affiliates. All rights reserved.
+ *  DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ *  This code is free software; you can redistribute it and/or modify it
+ *  under the terms of the GNU General Public License version 2 only, as
+ *  published by the Free Software Foundation.  Oracle designates this
+ *  particular file as subject to the "Classpath" exception as provided
+ *  by Oracle in the LICENSE file that accompanied this code.
+ *
+ *  This code is distributed in the hope that it will be useful, but WITHOUT
+ *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ *  version 2 for more details (a copy is included in the LICENSE file that
+ *  accompanied this code).
+ *
+ *  You should have received a copy of the GNU General Public License version
+ *  2 along with this work; if not, write to the Free Software Foundation,
+ *  Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ *   Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ *  or visit www.oracle.com if you need additional information or have any
+ *  questions.
+ *
+ */
+package jdk.incubator.foreign;
+
+import java.lang.constant.ConstantDesc;
+import java.lang.constant.ConstantDescs;
+import java.lang.constant.DynamicConstantDesc;
+import java.lang.constant.MethodHandleDesc;
+import java.util.Collections;
+import java.util.List;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.OptionalLong;
+import java.util.function.LongBinaryOperator;
+import java.util.stream.Collectors;
+
+/**
+ * A group layout is used to combine together multiple <em>member layouts</em>. There are two ways in which member layouts
+ * can be combined: if member layouts are laid out one after the other, the resulting group layout is said to be a <em>struct</em>
+ * (see {@link MemoryLayout#ofStruct(MemoryLayout...)}); conversely, if all member layouts are laid out at the same starting offset,
+ * the resulting group layout is said to be a <em>union</em> (see {@link MemoryLayout#ofUnion(MemoryLayout...)}).
+ *
+ * <p>
+ * This is a <a href="{@docRoot}/java.base/java/lang/doc-files/ValueBased.html">value-based</a>
+ * class; use of identity-sensitive operations (including reference equality
+ * ({@code ==}), identity hash code, or synchronization) on instances of
+ * {@code GroupLayout} may have unpredictable results and should be avoided.
+ * The {@code equals} method should be used for comparisons.
+ *
+ * @implSpec
+ * This class is immutable and thread-safe.
+ */
+public final class GroupLayout extends AbstractLayout {
+
+    /**
+     * The group kind.
+     */
+    enum Kind {
+        /**
+         * A 'struct' kind.
+         */
+        STRUCT("", MH_STRUCT, Long::sum),
+        /**
+         * A 'union' kind.
+         */
+        UNION("|", MH_UNION, Math::max);
+
+        final String delimTag;
+        final MethodHandleDesc mhDesc;
+        final LongBinaryOperator sizeOp;
+
+        Kind(String delimTag, MethodHandleDesc mhDesc, LongBinaryOperator sizeOp) {
+            this.delimTag = delimTag;
+            this.mhDesc = mhDesc;
+            this.sizeOp = sizeOp;
+        }
+
+        OptionalLong sizeof(List<MemoryLayout> elems) {
+            long size = 0;
+            for (MemoryLayout elem : elems) {
+                if (AbstractLayout.optSize(elem).isPresent()) {
+                    size = sizeOp.applyAsLong(size, elem.bitSize());
+                } else {
+                    return OptionalLong.empty();
+                }
+            }
+            return OptionalLong.of(size);
+        }
+
+        long alignof(List<MemoryLayout> elems) {
+            return elems.stream().mapToLong(MemoryLayout::bitAlignment).max() // max alignment in case we have member layouts
+                    .orElse(1); // or minimal alignment if no member layout is given
+        }
+    }
+
+    private final Kind kind;
+    private final List<MemoryLayout> elements;
+
+    GroupLayout(Kind kind, List<MemoryLayout> elements) {
+        this(kind, elements, kind.alignof(elements), Optional.empty());
+    }
+
+    GroupLayout(Kind kind, List<MemoryLayout> elements, long alignment, Optional<String> name) {
+        super(kind.sizeof(elements), alignment, name);
+        this.kind = kind;
+        this.elements = elements;
+    }
+
+    /**
+     * Returns the member layouts associated with this group.
+     *
+     * @apiNote the order in which member layouts are returned is the same order in which member layouts have
+     * been passed to one of the group layout factory methods (see {@link MemoryLayout#ofStruct(MemoryLayout...)},
+     * {@link MemoryLayout#ofUnion(MemoryLayout...)}).
+     *
+     * @return the member layouts associated with this group.
+     */
+    public List<MemoryLayout> memberLayouts() {
+        return Collections.unmodifiableList(elements);
+    }
+
+    @Override
+    public String toString() {
+        return decorateLayoutString(elements.stream()
+                .map(Object::toString)
+                .collect(Collectors.joining(kind.delimTag, "[", "]")));
+    }
+
+    /**
+     * Is this group layout a <em>struct</em>?
+     *
+     * @return true, if this group layout is a <em>struct</em>.
+     */
+    public boolean isStruct() {
+        return kind == Kind.STRUCT;
+    }
+
+    /**
+     * Is this group layout a <em>union</em>?
+     *
+     * @return true, if this group layout is a <em>union</em>.
+     */
+    public boolean isUnion() {
+        return kind == Kind.UNION;
+    }
+
+    @Override
+    public boolean equals(Object other) {
+        if (this == other) {
+            return true;
+        }
+        if (!super.equals(other)) {
+            return false;
+        }
+        if (!(other instanceof GroupLayout)) {
+            return false;
+        }
+        GroupLayout g = (GroupLayout)other;
+        return kind.equals(g.kind) && elements.equals(g.elements);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(super.hashCode(), kind, elements);
+    }
+
+    @Override
+    GroupLayout dup(long alignment, Optional<String> name) {
+        return new GroupLayout(kind, elements, alignment, name);
+    }
+
+    @Override
+    boolean hasNaturalAlignment() {
+        return alignment == kind.alignof(elements);
+    }
+
+    @Override
+    public Optional<DynamicConstantDesc<GroupLayout>> describeConstable() {
+        ConstantDesc[] constants = new ConstantDesc[1 + elements.size()];
+        constants[0] = kind.mhDesc;
+        for (int i = 0 ; i < elements.size() ; i++) {
+            constants[i + 1] = elements.get(i).describeConstable().get();
+        }
+        return Optional.of(DynamicConstantDesc.ofNamed(
+                    ConstantDescs.BSM_INVOKE, kind.name().toLowerCase(),
+                CD_GROUP_LAYOUT, constants));
+    }
+
+    //hack: the declarations below are to make javadoc happy; we could have used generics in AbstractLayout
+    //but that causes issues with javadoc, see JDK-8224052
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public GroupLayout withName(String name) {
+        return (GroupLayout)super.withName(name);
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public GroupLayout withBitAlignment(long alignmentBits) {
+        return (GroupLayout)super.withBitAlignment(alignmentBits);
+    }
+}