mfbt/IndexSequence.h
author Boris Zbarsky <bzbarsky@mit.edu>
Wed, 24 Jun 2015 00:42:46 -0700
changeset 250045 4267b74ee795e8127ffce4d45d00384cd8170130
parent 245102 bf2c8ae05278de6a2029a39a55e1b5069c7f4cfe
child 252586 91d6e262b662a0b4e47358665e222d3927337af9
permissions -rw-r--r--
Bug 1176083. Remove the now-dead code for the XPCOM version of setTimeout/setInterval. r=smaug I claim this code is dead because on the one hand it's no longer called from JS (because Window is always on WebIDL bindings, but on the other hand it can't really be called from C++ because it depends on examining the XPConnect call information. I think removing this completely, including from the IDL, is safe, because nothing directly returns nsIDOMJSWindow, so anyone using its vtable would have to QI to it and we're changing the IID.

/* -*- 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/. */

/* A utility for expanding a tuple into a variadic argument list.
 * Based on std::index_sequence. */

/**
 * Example usage:
 *
 * Problem:
 *
 *   You have a variadic function Foo:
 *
 *     template <typename... Args> void Foo(Args...);
 *
 *   And a variadic function Bar, which contains a tuple:
 *
 *     template <typename... Args>
 *     void Bar() {
 *       // ...
 *       Tuple<Args...> t;
 *     }
 *
 *   And inside Bar, you want to call Foo with the elements of the tuple as
 *   arguments to Foo.
 *
 *   You want to write:
 *
 *     Foo(Get<0>(t), Get<1>(t), ..., Get<N>(t))
 *
 *   but you can't literally write that, because N is different for different
 *   instantiations of Bar.
 *
 * Solution:
 *
 *   Write a helper function which takes the tuple, and an index sequence
 *   containing indices corresponding to the tuple indices.
 *
 *     template <typename... Args, size_t... Indices>
 *     void Helper(const Tuple<Args...>& t, IndexSequence<Indices>)
 *     {
 *       Foo(Get<Indices>(t)...);
 *     }
 *
 *   Assuming 'Indices...' are 0, 1, ..., N - 1, where N is the size of the
 *   tuple, pack expansion will expand the pack 'Get<Indices>(t)...' to
 *   'Get<0>(t), Get<1>(t), ..., Get<N>(t)'.
 *
 *   Finally, call the helper, creating the index sequence to pass in like so:
 *
 *     template <typename... Args>
 *     void Bar() {
 *       // ...
 *       Tuple<Args...> t;
 *       Helper(t, typename IndexSequenceFor<Args...>::Type());
 *     }
 */

#ifndef mozilla_IndexSequence_h
#define mozilla_IndexSequence_h

#include "mozilla/Attributes.h"

#include <stddef.h>

namespace mozilla {

/**
 * Represents a compile-time sequence of integer indices.
 */
template<size_t... Indices>
struct IndexSequence
{
  static MOZ_CONSTEXPR size_t Size() { return sizeof...(Indices); }
};

namespace detail {

// Helpers used by MakeIndexSequence.

template<size_t... Indices>
struct IndexTuple
{
  typedef IndexTuple<Indices..., sizeof...(Indices)> Next;
};

// Builds IndexTuple<0, 1, ..., N - 1>.
template<size_t N>
struct BuildIndexTuple
{
  typedef typename BuildIndexTuple<N - 1>::Type::Next Type;
};

template<>
struct BuildIndexTuple<0>
{
  typedef IndexTuple<> Type;
};

template<size_t N, typename IndexTuple>
struct MakeIndexSequenceImpl;

template<size_t N, size_t... Indices>
struct MakeIndexSequenceImpl<N, IndexTuple<Indices...>>
{
  typedef IndexSequence<Indices...> Type;
};

}  // namespace detail

/**
 * A utility for building an IndexSequence of consecutive indices.
 * MakeIndexSequence<N>::Type evaluates to IndexSequence<0, 1, .., N - 1>.
 * Note: unlike std::make_index_sequence, this is not an alias template
 * to work around bugs in MSVC 2013.
 */
template<size_t N>
struct MakeIndexSequence
{
  typedef typename detail::MakeIndexSequenceImpl<N,
    typename detail::BuildIndexTuple<N>::Type>::Type Type;
};

/**
 * A utility for building an IndexSequence of consecutive indices
 * corresponding to a variadic argument list.
 * IndexSequenceFor<Types...> evaluates to IndexSequence<0, 1, ..., N - 1>
 * where N is the number of types in Types.
 * Note: unlike std::index_sequence_for, this is not an alias template
 * to work around bugs in MSVC 2013.
 */
template<typename... Types>
struct IndexSequenceFor
{
  typedef typename MakeIndexSequence<sizeof...(Types)>::Type Type;
};

} // namespace mozilla

#endif /* mozilla_IndexSequence_h */