Benjamin Bannier created MESOS-7410:
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Summary: Make it harder to ignore errors returned from functions.
Key: MESOS-7410
URL: https://issues.apache.org/jira/browse/MESOS-7410
Project: Mesos
Issue Type: Improvement
Reporter: Benjamin Bannier
Mesos (or more specifically stout) uses a number of types which can capture
either a value or an error (e.g., {{Try}} or {{Result}}). These are used
similar to exceptions, but in contrast to exceptions, the possible errors are
part of the function's types. It is also possible to (implicitly) ignore errors
return from functions producing such values (this is not possible with
exceptions).
C\+\+11 introduced a generalized syntax for attributes which makes it possible
to add attributes to types. C++17 standardized an attribute {{nodiscard}} which
{quote}
Appears in a function declaration, enumeration declaration, or class
declaration. If a function declared nodiscard or a function returning an
enumeration or class declared nodiscard by value is called from a
discarded-value expression other than a cast to void, the compiler is
encouraged to issue a warning.
{quote}
With that it is possible to annotate types with a {{nodiscard}} attribute which
was not possible with e.g., GNU attributes, e.g.,
{code}
class [[nodiscard]] Try;
{code}
We should annotate our error types with {{nodiscard}} to make sure errors are
not missed.
This will likely require updating call sites to handle currently ignored return
values (this appears more widespread in users of e.g., {{os::close}} or
{{os::sleep}}). Since compilers might emit errors for unknown attributes we
should also prevent breaking a build on compilers not supporting this attribute.
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