Update TotW #120 to reflect the OSS availability of absl::Cleanup and absl::Status

_posts/2018-04-20-totw-120.md

@@ -10,17 +10,17 @@ order: "120"
 
 Originally posted as TotW #120 on August 16, 2012
 
-*by Samuel Benzaquen, [([email protected])](mailto:sbenza@gmail.com)*
+_by Samuel Benzaquen, [([email protected])](mailto:sbenza@google.com)_
 
-Let's suppose you have a code snippet like below, which relies on an RAII
-cleanup function, which seems to be working as expected:
+Let's suppose you have a code snippet like below, which relies on a scope
+guard utility, which seems to be working as expected:
 
 ```c++
-MyStatus DoSomething() {
-  MyStatus status;
-  auto log_on_error = RunWhenOutOfScope([&status] {
+absl::Status DoSomething() {
+  absl::Status status;
+  absl::Cleanup log_on_error = [&status] {
     if (!status.ok()) LOG(ERROR) << status;
-  });
+  };
   status = DoA();
   if (!status.ok()) return status;
   status = DoB();
@@ -32,7 +32,8 @@ MyStatus DoSomething() {
 ```
 
 A refactor changes the last line from `return status;` to
-`return MyStatus();` and suddenly the code stopped logging errors.
+`return absl::OkStatus();` and suddenly the code stopped logging
+errors.
 
 What is going on?
 
@@ -56,16 +57,16 @@ There are 2 different optimizations on return statements that can modify the
 behavior of our original code snippet: NRVO (See [TotW #11](/tips/11)) and
 implicit moves.
 
-The *before* code worked because copy elision is taking place and the
+The _before_ code worked because copy elision is taking place and the
 `return` statement is not actually doing any work. The variable `status` is
 already constructed in the return address and the cleanup object is seeing this
-unique instance of the `MyStatus` object _after_ the return statement.
+unique instance of the `absl::Status` object _after_ the return statement.
 
-In the *after* code, copy elision is not being applied and the returned variable
-is being moved into the return value. `RunWhenOutOfScope()` runs after the
-move operation is done and it is seeing a moved-from `MyStatus` object.
+In the _after_ code, copy elision is not being applied and the returned variable
+is being moved into the return value. `absl::Cleanup` runs after the move
+operation is done and it is seeing a moved-from `absl::Status` object.
 
-Note that the *before* code was not correct either, as it relies on the copy
+Note that the _before_ code was not correct either, as it relies on the copy
 elision optimization for correctness. We encourage you to rely on copy elision
 for performance (See [TotW #24](/tips/24)), but not correctness. After all,
 copy elision is an _optional_ optimization and compiler options or quality of
@@ -81,8 +82,8 @@ processing, and one that calls the first one and does the post-processing (ie
 logging on error). Eg:
 
 ```c++
-MyStatus DoSomething() {
-  MyStatus status;
+absl::Status DoSomething() {
+  absl::Status status;
   status = DoA();
   if (!status.ok()) return status;
   status = DoB();
@@ -91,8 +92,8 @@ MyStatus DoSomething() {
   if (!status.ok()) return status;
   return status;
 }
-MyStatus DoSomethingAndLog() {
-  MyStatus status = DoSomething();
+absl::Status DoSomethingAndLog() {
+  absl::Status status = DoSomething();
   if (!status.ok()) LOG(ERROR) << status;
   return status;
 }
@@ -103,16 +104,16 @@ optimizations instead. That would force a copy to be made all the time and the
 post-processing will not see a moved-from value. E.g.:
 
 ```c++
-MyStatus DoSomething() {
-  MyStatus status_no_nrvo;
+absl::Status DoSomething() {
+  absl::Status status_no_nrvo;
   // 'status' is a reference so NRVO and all associated optimizations
   // will be disabled.
   // The 'return status;' statements will always copy the object and Logger
   // will always see the correct value.
-  MyStatus& status = status_no_nrvo;
-  auto log_on_error = RunWhenOutOfScope([&status] {
+  absl::Status& status = status_no_nrvo;
+  absl::Cleanup log_on_error = [&status] {
     if (!status.ok()) LOG(ERROR) << status;
-  });
+  };
   status = DoA();
   if (!status.ok()) return status;
   status = DoB();