absl/log/die_if_null.h

0001 // Copyright 2022 The Abseil Authors.
0002 //
0003 // Licensed under the Apache License, Version 2.0 (the "License");
0004 // you may not use this file except in compliance with the License.
0005 // You may obtain a copy of the License at
0006 //
0007 //      https://www.apache.org/licenses/LICENSE-2.0
0008 //
0009 // Unless required by applicable law or agreed to in writing, software
0010 // distributed under the License is distributed on an "AS IS" BASIS,
0011 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
0012 // See the License for the specific language governing permissions and
0013 // limitations under the License.
0014 //
0015 // -----------------------------------------------------------------------------
0016 // File: log/die_if_null.h
0017 // -----------------------------------------------------------------------------
0018 //
0019 // This header declares macro `ABSL_DIE_IF_NULL`.
0020
0021 #ifndef ABSL_LOG_DIE_IF_NULL_H_
0022 #define ABSL_LOG_DIE_IF_NULL_H_
0023
0024 #include <stdint.h>
0025
0026 #include <utility>
0027
0028 #include "absl/base/attributes.h"
0029 #include "absl/base/config.h"
0030 #include "absl/base/optimization.h"
0031
0032 // ABSL_DIE_IF_NULL()
0033 //
0034 // `ABSL_DIE_IF_NULL` behaves as `CHECK_NE` against `nullptr` but *also*
0035 // "returns" its argument.  It is useful in initializers where statements (like
0036 // `CHECK_NE`) can't be used.  Outside initializers, prefer `CHECK` or
0037 // `CHECK_NE`. `ABSL_DIE_IF_NULL` works for both raw pointers and (compatible)
0038 // smart pointers including `std::unique_ptr` and `std::shared_ptr`; more
0039 // generally, it works for any type that can be compared to nullptr_t.  For
0040 // types that aren't raw pointers, `ABSL_DIE_IF_NULL` returns a reference to
0041 // its argument, preserving the value category. Example:
0042 //
0043 //   Foo() : bar_(ABSL_DIE_IF_NULL(MethodReturningUniquePtr())) {}
0044 //
0045 // Use `CHECK(ptr)` or `CHECK(ptr != nullptr)` if the returned pointer is
0046 // unused.
0047 #define ABSL_DIE_IF_NULL(val) \
0048   ::absl::log_internal::DieIfNull(__FILE__, __LINE__, #val, (val))
0049
0050 namespace absl {
0051 ABSL_NAMESPACE_BEGIN
0052 namespace log_internal {
0053
0054 // Crashes the process after logging `exprtext` annotated at the `file` and
0055 // `line` location. Called when `ABSL_DIE_IF_NULL` fails. Calling this function
0056 // generates less code than its implementation would if inlined, for a slight
0057 // code size reduction each time `ABSL_DIE_IF_NULL` is called.
0058 [[noreturn]] ABSL_ATTRIBUTE_NOINLINE void DieBecauseNull(
0059     const char* file, int line, const char* exprtext);
0060
0061 // Helper for `ABSL_DIE_IF_NULL`.
0062 template <typename T>
0063 ABSL_MUST_USE_RESULT T DieIfNull(const char* file, int line,
0064                                  const char* exprtext, T&& t) {
0065   if (ABSL_PREDICT_FALSE(t == nullptr)) {
0066     // Call a non-inline helper function for a small code size improvement.
0067     DieBecauseNull(file, line, exprtext);
0068   }
0069   return std::forward<T>(t);
0070 }
0071
0072 }  // namespace log_internal
0073 ABSL_NAMESPACE_END
0074 }  // namespace absl
0075
0076 #endif  // ABSL_LOG_DIE_IF_NULL_H_