idmap2: replace std::pair<bool, T> with Result<T>

Introduce a new type Result<T> to indicate if an operation succeeded or
not, and if it did, to hold the return value of the operation. This is
the same as how std::pair<bool, T> is already used in the codebase, so
replace all instances with Result<T> to improve clarity.

Result<T> is simply an alias for std::optional<T>. The difference is
semantic: use Result<T> as the return value for functions that can fail,
use std::optional<T> when values are truly optional. This is modelled
after Rust's std::result and std::option.

A future change may graduate Result<T> to a proper class which can hold
additional details on why an operation failed, such as a string or an
error code. As a special case, continue to use std::unique_ptr<T>
instead of Result<std::unique_ptr<T>> for now: the latter would increase
code complexity without added benefit.

Test: make idmap2_tests
Change-Id: I2a8355107ed2b6485409e5e655a84cf1e20b9911

1 files changed, 3 insertions, 3 deletions

diff --git a/cmds/idmap2/libidmap2/ZipFile.cpp b/cmds/idmap2/libidmap2/ZipFile.cpp
index 3f2079a380d6..9fb611dd8e8d 100644
--- a/cmds/idmap2/libidmap2/ZipFile.cpp
+++ b/cmds/idmap2/libidmap2/ZipFile.cpp
@@ -16,8 +16,8 @@
 
 #include <memory>
 #include <string>
-#include <utility>
 
+#include "idmap2/Result.h"
 #include "idmap2/ZipFile.h"
 
 namespace android {
@@ -57,10 +57,10 @@ std::unique_ptr<const MemoryChunk> ZipFile::Uncompress(const std::string& entryP
   return chunk;
 }
 
-std::pair<bool, uint32_t> ZipFile::Crc(const std::string& entryPath) const {
+Result<uint32_t> ZipFile::Crc(const std::string& entryPath) const {
   ::ZipEntry entry;
   int32_t status = ::FindEntry(handle_, ::ZipString(entryPath.c_str()), &entry);
-  return std::make_pair(status == 0, entry.crc32);
+  return status == 0 ? Result<uint32_t>(entry.crc32) : kResultError;
 }
 
 }  // namespace idmap2