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platform_system_core/init/result.h

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init: introduce Result<T> for return values and error handling init tries to propagate error information up to build context before logging errors. This is a good thing, however too often init has the overly verbose paradigm for error handling, below: bool CalculateResult(const T& input, U* output, std::string* err) bool CalculateAndUseResult(const T& input, std::string* err) { U output; std::string calculate_result_err; if (!CalculateResult(input, &output, &calculate_result_err)) { *err = "CalculateResult " + input + " failed: " + calculate_result_err; return false; } UseResult(output); return true; } Even more common are functions that return only true/false but also require passing a std::string* err in order to see the error message. This change introduces a Result<T> that is use to either hold a successful return value of type T or to hold an error message as a std::string. If the functional only returns success or a failure with an error message, Result<Success> may be used. The classes Error and ErrnoError are used to indicate a failed Result<T>. A successful Result<T> is constructed implicitly from any type that can be implicitly converted to T or from the constructor arguments for T. This allows you to return a type T directly from a function that returns Result<T>. Error and ErrnoError are used to construct a Result<T> has failed. Each of these classes take an ostream as an input and are implicitly cast to a Result<T> containing that failure. ErrnoError() additionally appends ": " + strerror(errno) to the end of the failure string to aid in interacting with C APIs. The end result is that the above code snippet is turned into the much clearer example below: Result<U> CalculateResult(const T& input); Result<Success> CalculateAndUseResult(const T& input) { auto output = CalculateResult(input); if (!output) { return Error() << "CalculateResult " << input << " failed: " << output.error(); } UseResult(*output); return Success(); } This change also makes this conversion for some of the util.cpp functions that used the old paradigm. Test: boot bullhead, init unit tests Merged-In: I1e7d3a8820a79362245041251057fbeed2f7979b Change-Id: I1e7d3a8820a79362245041251057fbeed2f7979b
2017-08-03 21:54:07 +02:00
/*
* Copyright (C) 2017 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.
*/
init: replace Result<> with expected<> Android-base has an implementation of the future std::expected<>. This provides the same baseline functionality as Result<>, so use it instead of our own version. Bug: 132145659 Test: boot, init unit tests Change-Id: I11e61bcb5719b262a6420483ed51a762826a9e23
2019-05-17 01:54:49 +02:00
#pragma once
init: introduce Result<T> for return values and error handling init tries to propagate error information up to build context before logging errors. This is a good thing, however too often init has the overly verbose paradigm for error handling, below: bool CalculateResult(const T& input, U* output, std::string* err) bool CalculateAndUseResult(const T& input, std::string* err) { U output; std::string calculate_result_err; if (!CalculateResult(input, &output, &calculate_result_err)) { *err = "CalculateResult " + input + " failed: " + calculate_result_err; return false; } UseResult(output); return true; } Even more common are functions that return only true/false but also require passing a std::string* err in order to see the error message. This change introduces a Result<T> that is use to either hold a successful return value of type T or to hold an error message as a std::string. If the functional only returns success or a failure with an error message, Result<Success> may be used. The classes Error and ErrnoError are used to indicate a failed Result<T>. A successful Result<T> is constructed implicitly from any type that can be implicitly converted to T or from the constructor arguments for T. This allows you to return a type T directly from a function that returns Result<T>. Error and ErrnoError are used to construct a Result<T> has failed. Each of these classes take an ostream as an input and are implicitly cast to a Result<T> containing that failure. ErrnoError() additionally appends ": " + strerror(errno) to the end of the failure string to aid in interacting with C APIs. The end result is that the above code snippet is turned into the much clearer example below: Result<U> CalculateResult(const T& input); Result<Success> CalculateAndUseResult(const T& input) { auto output = CalculateResult(input); if (!output) { return Error() << "CalculateResult " << input << " failed: " << output.error(); } UseResult(*output); return Success(); } This change also makes this conversion for some of the util.cpp functions that used the old paradigm. Test: boot bullhead, init unit tests Merged-In: I1e7d3a8820a79362245041251057fbeed2f7979b Change-Id: I1e7d3a8820a79362245041251057fbeed2f7979b
2017-08-03 21:54:07 +02:00
init: replace Result<Success> with Result<void> Now that Result<T> is actually expected<T, ...>, and the expected proposal states expected<void, ...> as the way to indicate an expected object that returns either successfully with no object or an error, let's move init's Result<Success> to the preferred Result<void>. Bug: 132145659 Test: boot, init unit tests Change-Id: Ib2f98396d8e6e274f95a496fcdfd8341f77585ee
2019-06-10 20:08:01 +02:00
// The implementation of this file has moved to android-base. This file remains since historically,
// these classes were a part of init.
Move result.h from init to libbase The Result, Error, ErrnoError are quite generic. Moving them from init to libbase so that they can be used from other places. Bug: 132145659 Test: libbase_test Change-Id: Id774a587f74380fadd7a0fc88c0aa892c3d9a489
2019-05-30 20:43:34 +02:00
#include <android-base/result.h>
init: introduce Result<T> for return values and error handling init tries to propagate error information up to build context before logging errors. This is a good thing, however too often init has the overly verbose paradigm for error handling, below: bool CalculateResult(const T& input, U* output, std::string* err) bool CalculateAndUseResult(const T& input, std::string* err) { U output; std::string calculate_result_err; if (!CalculateResult(input, &output, &calculate_result_err)) { *err = "CalculateResult " + input + " failed: " + calculate_result_err; return false; } UseResult(output); return true; } Even more common are functions that return only true/false but also require passing a std::string* err in order to see the error message. This change introduces a Result<T> that is use to either hold a successful return value of type T or to hold an error message as a std::string. If the functional only returns success or a failure with an error message, Result<Success> may be used. The classes Error and ErrnoError are used to indicate a failed Result<T>. A successful Result<T> is constructed implicitly from any type that can be implicitly converted to T or from the constructor arguments for T. This allows you to return a type T directly from a function that returns Result<T>. Error and ErrnoError are used to construct a Result<T> has failed. Each of these classes take an ostream as an input and are implicitly cast to a Result<T> containing that failure. ErrnoError() additionally appends ": " + strerror(errno) to the end of the failure string to aid in interacting with C APIs. The end result is that the above code snippet is turned into the much clearer example below: Result<U> CalculateResult(const T& input); Result<Success> CalculateAndUseResult(const T& input) { auto output = CalculateResult(input); if (!output) { return Error() << "CalculateResult " << input << " failed: " << output.error(); } UseResult(*output); return Success(); } This change also makes this conversion for some of the util.cpp functions that used the old paradigm. Test: boot bullhead, init unit tests Merged-In: I1e7d3a8820a79362245041251057fbeed2f7979b Change-Id: I1e7d3a8820a79362245041251057fbeed2f7979b
2017-08-03 21:54:07 +02:00
Move result.h from init to libbase The Result, Error, ErrnoError are quite generic. Moving them from init to libbase so that they can be used from other places. Bug: 132145659 Test: libbase_test Change-Id: Id774a587f74380fadd7a0fc88c0aa892c3d9a489
2019-05-30 20:43:34 +02:00
using android::base::ErrnoError;
using android::base::Error;
using android::base::Result;
using android::base::ResultError;
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