1 files changed, 121 insertions, 0 deletions
diff --git a/js/src/gc/IteratorUtils.h b/js/src/gc/IteratorUtils.h
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+++ b/js/src/gc/IteratorUtils.h
@@ -0,0 +1,121 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef gc_IteratorUtils_h
+#define gc_IteratorUtils_h
+
+#include "mozilla/Array.h"
+#include "mozilla/Maybe.h"
+
+#include <initializer_list>
+
+namespace js {
+
+/*
+ * Create an iterator that yields the values from IteratorB(a) for all a in
+ * IteratorA(). Equivalent to nested for loops over IteratorA and IteratorB
+ * where IteratorB is constructed with a value from IteratorA.
+ */
+template <typename IteratorA, typename IteratorB>
+class NestedIterator {
+  using T = decltype(std::declval<IteratorB>().get());
+
+  IteratorA a;
+  mozilla::Maybe<IteratorB> b;
+
+ public:
+  template <typename... Args>
+  explicit NestedIterator(Args&&... args) : a(std::forward<Args>(args)...) {
+    settle();
+  }
+
+  bool done() const { return b.isNothing(); }
+
+  T get() const {
+    MOZ_ASSERT(!done());
+    return b.ref().get();
+  }
+
+  void next() {
+    MOZ_ASSERT(!done());
+    b->next();
+    if (b->done()) {
+      b.reset();
+      a.next();
+      settle();
+    }
+  }
+
+  const IteratorB& ref() const { return *b; }
+
+  operator T() const { return get(); }
+
+  T operator->() const { return get(); }
+
+ private:
+  void settle() {
+    MOZ_ASSERT(b.isNothing());
+    while (!a.done()) {
+      b.emplace(a.get());
+      if (!b->done()) {
+        break;
+      }
+      b.reset();
+      a.next();
+    }
+  }
+};
+
+/*
+ * An iterator the yields values from each of N of instances of Iterator in
+ * sequence.
+ */
+template <typename Iterator, size_t N>
+class ChainedIterator {
+  using T = decltype(std::declval<Iterator>().get());
+
+  mozilla::Array<Iterator, N> iterators;
+  size_t index = 0;
+
+ public:
+  template <typename... Args>
+  MOZ_IMPLICIT ChainedIterator(Args&&... args)
+      : iterators(Iterator(std::forward<Args>(args))...) {
+    static_assert(N > 1);
+    settle();
+  }
+
+  bool done() const { return index == N; }
+
+  void next() {
+    MOZ_ASSERT(!done());
+    iterators[index].next();
+    settle();
+  }
+
+  T get() const {
+    MOZ_ASSERT(!done());
+    return iterators[index].get();
+  }
+
+  operator T() const { return get(); }
+  T operator->() const { return get(); }
+
+ private:
+  void settle() {
+    MOZ_ASSERT(!done());
+    while (iterators[index].done()) {
+      index++;
+      if (done()) {
+        break;
+      }
+    }
+  }
+};
+
+} /* namespace js */
+
+#endif  // gc_IteratorUtils_h