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products/Sources/formale Sprachen/C/Firefox/mfbt/ (Firefox Browser Version 153.0.1^©) Datei vom 27.6.2026 mit Größe 2 kB

Quelle OperatorNewExtensions.h

Sprache: C

/* 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 version of |operator new| that eschews mandatory null-checks. */

#ifndef mozilla_OperatorNewExtensions_h
#define mozilla_OperatorNewExtensions_h

#include "mozilla/Assertions.h"

// Credit goes to WebKit for this implementation, cf.
// https://bugs.webkit.org/show_bug.cgi?id=74676
namespace mozilla {
enum NotNullTag {
  KnownNotNull,
};
}  // namespace mozilla

/*
* The logic here is a little subtle.  [expr.new] states that if the allocation
* function being called returns null, then object initialization must not be
* done, and the entirety of the new expression must return null.  Non-throwing
* (noexcept) functions are defined to return null to indicate failure.  The
* standard placement operator new is defined in such a way, and so it requires
* a null check, even when that null check would be extraneous.  Functions
* declared without such a specification are defined to throw std::bad_alloc if
* they fail, and return a non-null pointer otherwise.  We compile without
* exceptions, so any placement new overload we define that doesn't declare
* itself as noexcept must therefore avoid generating a null check.  Below is
* just such an overload.
*
* You might think that MOZ_NONNULL might perform the same function, but
* MOZ_NONNULL isn't supported on all of our compilers, and even when it is
* supported, doesn't work on all the versions we support.  And even keeping
* those limitations in mind, we can't put MOZ_NONNULL on the global,
* standardized placement new function in any event.
*
* We deliberately don't add MOZ_NONNULL(3) to tag |p| as non-null, to benefit
* hypothetical static analyzers.  Doing so makes |MOZ_ASSERT(p)|'s internal
* test vacuous, and some compilers warn about such vacuous tests.
*/
inline void* operator new(size_t, mozilla::NotNullTag, void* p) {
  MOZ_ASSERT(p);
  return p;
}

#endif  // mozilla_OperatorNewExtensions_h

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