absl/log/die_if_null.h

// Copyright 2022 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// -----------------------------------------------------------------------------
// File: log/die_if_null.h
// -----------------------------------------------------------------------------
//
// This header declares macro `ABSL_DIE_IF_NULL`.

#ifndef ABSL_LOG_DIE_IF_NULL_H_
#define ABSL_LOG_DIE_IF_NULL_H_

#include <stdint.h>

#include <utility>

#include "absl/base/attributes.h"
#include "absl/base/config.h"
#include "absl/base/optimization.h"

// ABSL_DIE_IF_NULL()
//
// `ABSL_DIE_IF_NULL` behaves as `CHECK_NE` against `nullptr` but *also*
// "returns" its argument.  It is useful in initializers where statements (like
// `CHECK_NE`) can't be used.  Outside initializers, prefer `CHECK` or
// `CHECK_NE`. `ABSL_DIE_IF_NULL` works for both raw pointers and (compatible)
// smart pointers including `std::unique_ptr` and `std::shared_ptr`; more
// generally, it works for any type that can be compared to nullptr_t.  For
// types that aren't raw pointers, `ABSL_DIE_IF_NULL` returns a reference to
// its argument, preserving the value category. Example:
//
//   Foo() : bar_(ABSL_DIE_IF_NULL(MethodReturningUniquePtr())) {}
//
// Use `CHECK(ptr)` or `CHECK(ptr != nullptr)` if the returned pointer is
// unused.
#define ABSL_DIE_IF_NULL(val) \
  ::absl::log_internal::DieIfNull(__FILE__, __LINE__, #val, (val))

namespace absl {
ABSL_NAMESPACE_BEGIN
namespace log_internal {

// Crashes the process after logging `exprtext` annotated at the `file` and
// `line` location. Called when `ABSL_DIE_IF_NULL` fails. Calling this function
// generates less code than its implementation would if inlined, for a slight
// code size reduction each time `ABSL_DIE_IF_NULL` is called.
[[noreturn]] ABSL_ATTRIBUTE_NOINLINE void DieBecauseNull(
    const char* file, int line, const char* exprtext);

// Helper for `ABSL_DIE_IF_NULL`.
template <typename T>
ABSL_MUST_USE_RESULT T DieIfNull(const char* file, int line,
                                 const char* exprtext, T&& t) {
  if (ABSL_PREDICT_FALSE(t == nullptr)) {
    // Call a non-inline helper function for a small code size improvement.
    DieBecauseNull(file, line, exprtext);
  }
  return std::forward<T>(t);
}

}  // namespace log_internal
ABSL_NAMESPACE_END
}  // namespace absl

#endif  // ABSL_LOG_DIE_IF_NULL_H_