xpcom/ds/SimpleEnumerator.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef mozilla_SimpleEnumerator_h
   8 #define mozilla_SimpleEnumerator_h
   9
  10 #include "nsCOMPtr.h"
  11 #include "nsISimpleEnumerator.h"
  12
  13 namespace mozilla {
  14
  15 /**
  16  * A wrapper class around nsISimpleEnumerator to support ranged iteration. This
  17  * requires every element in the enumeration to implement the same interface, T.
  18  * If any element does not implement this interface, the enumeration ends at
  19  * that element, and triggers an assertion in debug builds.
  20  *
  21  * Typical usage looks something like:
  22  *
  23  *   for (auto& docShell : SimpleEnumerator<nsIDocShell>(docShellEnum)) {
  24  *     docShell.LoadURI(...);
  25  *   }
  26  */
  27
  28 template <typename T>
  29 class SimpleEnumerator final {
  30  public:
  31   explicit SimpleEnumerator(nsISimpleEnumerator* aEnum) : mEnum(aEnum) {}
  32
  33   class Entry {
  34    public:
  35     explicit Entry(T* aPtr) : mPtr(aPtr) {}
  36
  37     explicit Entry(nsISimpleEnumerator& aEnum) : mEnum(&aEnum) { ++*this; }
  38
  39     const nsCOMPtr<T>& operator*() {
  40       MOZ_ASSERT(mPtr);
  41       return mPtr;
  42     }
  43
  44     Entry& operator++() {
  45       MOZ_ASSERT(mEnum);
  46       nsCOMPtr<nsISupports> next;
  47       if (NS_SUCCEEDED(mEnum->GetNext(getter_AddRefs(next)))) {
  48         mPtr = do_QueryInterface(next);
  49         MOZ_ASSERT(mPtr);
  50       } else {
  51         mPtr = nullptr;
  52       }
  53       return *this;
  54     }
  55
  56     bool operator!=(const Entry& aOther) const { return mPtr != aOther.mPtr; }
  57
  58    private:
  59     nsCOMPtr<T> mPtr;
  60     nsCOMPtr<nsISimpleEnumerator> mEnum;
  61   };
  62
  63   Entry begin() { return Entry(*mEnum); }
  64
  65   Entry end() { return Entry(nullptr); }
  66
  67  private:
  68   nsCOMPtr<nsISimpleEnumerator> mEnum;
  69 };
  70
  71 }  // namespace mozilla
  72
  73 #endif  // mozilla_SimpleEnumerator_h