gecko-dev/ipc/glue/IPDLStructMember.h
Nika Layzell fc898b85f5 Bug 1814683 - Part 4: Allow IPDL structs to contain non-default-constructable types, r=ipc-reviewers,jld
Previously, we would always generate a default constructor for IPDL structs
which explicitly initializes every member. This would require members to have
default initializers statically. With the new approach, each member is
individually wrapped with a template parameter which will try to ensure value
initiaization, and the default constructor is implemented with `= default;`.

The default constructor will produce a warning on clang if it is implicitly
deleted, so that warning is also suppressed.

Differential Revision: https://phabricator.services.mozilla.com/D168881
2023-03-20 15:40:34 +00:00

38 lines
1.3 KiB
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/* -*- 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 mozilla_ipc_IPDLStructMember_h
#define mozilla_ipc_IPDLStructMember_h
#include <type_traits>
#include <utility>
#include "mozilla/Attributes.h"
namespace mozilla::ipc {
// For types which are trivially default constructible, like `int`, force the
// value constructor by wrapping the type in this struct. This is an
// implementation detail which will be hidden by the generated IPDL compiler
// code.
template <typename T>
struct IPDLStructMemberWrapper {
template <typename... Args>
MOZ_IMPLICIT IPDLStructMemberWrapper(Args&&... aArgs)
: mVal(std::forward<Args>(aArgs)...) {}
MOZ_IMPLICIT operator T&() { return mVal; }
MOZ_IMPLICIT operator const T&() const { return mVal; }
T mVal{};
};
template <typename T>
using IPDLStructMember =
std::conditional_t<std::is_trivially_default_constructible_v<T>,
IPDLStructMemberWrapper<T>, T>;
} // namespace mozilla::ipc
#endif // mozilla_ipc_IPDLStructMember_h