pw::Result
is a convenient wrapper around returning a Status along side some
data when the status is OK. This is meant for returning lightweight result
types or references to larger results.
pw::Result
is compatible with PW_TRY
and PW_TRY_ASSIGN
, for example:
#include "pw_status/try.h"
#include "pw_result/result.h"
pw::Result<int> GetAnswer(); // Example function.
pw::Status UseAnswer() {
const pw::Result<int> answer = GetAnswer();
if (!answer.ok()) {
return answer.status();
}
if (answer.value() == 42) {
WhatWasTheUltimateQuestion();
}
return pw::OkStatus();
}
pw::Status UseAnswerWithTry() {
const pw::Result<int> answer = GetAnswer();
PW_TRY(answer.status());
if (answer.value() == 42) {
WhatWasTheUltimateQuestion();
}
return pw::OkStatus();
}
pw::Status UseAnswerWithTryAssign() {
PW_TRY_ASSIGN(const int answer, GetAnswer());
if (answer == 42) {
WhatWasTheUltimateQuestion();
}
return pw::OkStatus();
}
pw::Result
can be used to directly access the contained type:
#include "pw_result/result.h"
pw::Result<Foo> foo = TryCreateFoo();
if (foo.ok()) {
foo->DoBar();
}
or in C++17:
if (pw::Result<Foo> foo = TryCreateFoo(); foo.ok()) {
foo->DoBar();
}
See Abseil's StatusOr for guidance on using a similar type.
Warning
Be careful not to use larger types by value as this can quickly consume unnecessary stack.
Warning
This module is experimental. Its impact on code size and stack usage has not yet been profiled. Use at your own risk.
Works with C++14, but some features require C++17.
The table below showcases the difference in size between functions returning a Status with an output pointer, and functions returning a Result, in various situations.
Note that these are simplified examples which do not necessarily reflect the usage of Result in real code. Make sure to always run your own size reports to check if Result is suitable for you.
To enable pw_result
for Zephyr add CONFIG_PIGWEED_RESULT=y
to the
project's configuration.