idmap2: introduce improved Result class
Add a new version of the Result class that functions like the old
Result, but in case of an error, also encodes a string detailing the
error. This will allow us to write the following type of code:
Result<Foo> CreateFoo() {
if (...) {
return Error("errno=%d", errno());
}
return Foo(...);
}
auto foo = CreateFoo();
if (!foo) {
std::cerr << "error: " << foo.GetErrorMessage() << std::endl;
abort();
}
std::cout << "foo=" << *foo << std::endl;
This commit only adds the new Result class. A later change will replace
uses of the old version.
Test: make idmap2_tests
Change-Id: I674d8a06866402adedf85f8514400f25840d5eda
diff --git a/cmds/idmap2/libidmap2/Result.cpp b/cmds/idmap2/libidmap2/Result.cpp
new file mode 100644
index 0000000..a5c9999
--- /dev/null
+++ b/cmds/idmap2/libidmap2/Result.cpp
@@ -0,0 +1,41 @@
+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * 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
+ *
+ * http://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.
+ */
+
+#include <cstdarg>
+
+#include "android-base/stringprintf.h"
+
+#include "idmap2/Result.h"
+
+namespace android::idmap2 {
+
+v2::Error::Error(const char* fmt, ...) {
+ va_list ap;
+ va_start(ap, fmt);
+ base::StringAppendV(&msg_, fmt, ap);
+ va_end(ap);
+}
+
+v2::Error::Error(const Error& parent, const char* fmt, ...) : msg_(parent.msg_) {
+ msg_.append(" -> ");
+
+ va_list ap;
+ va_start(ap, fmt);
+ base::StringAppendV(&msg_, fmt, ap);
+ va_end(ap);
+}
+
+} // namespace android::idmap2