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https://issues.apache.org/jira/browse/MESOS-1008?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13909002#comment-13909002
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Dominic Hamon commented on MESOS-1008:
--------------------------------------
Changes to Option:
https://reviews.apache.org/r/18383/
https://reviews.apache.org/r/18384/
https://reviews.apache.org/r/18386/
> Reduce copying in stout / libprocess primitives {Try, Option, Result, Future}.
> ------------------------------------------------------------------------------
>
> Key: MESOS-1008
> URL: https://issues.apache.org/jira/browse/MESOS-1008
> Project: Mesos
> Issue Type: Improvement
> Reporter: Benjamin Mahler
> Assignee: Benjamin Mahler
>
> The following will discuss {{Try}}, but the same applies to {{Option}} and
> {{Result}}.
> Currently retrieving the value from a {{Try}} requires a copy:
> {code}
> T get() const { ... return *t; }
> {code}
> Instead, we can return a const&:
> {code}
> const T& get() const { ... return *t; }
> {code}
> For existing callers, this should be fairly seamless:
> {code}
> const T& t = try.get(); // No change needed.
> T t = try.get(); // No change needed, T is already required to be copyable.
> try.get().mutator(); // Will no longer compile, but we should not allow
> this anyway!
> {code}
> {code}
> const T& t = try.get();
> try = T(); // t is now garbage!
> t.foo(); // No longer works.
> {code}
> The last case is the most concerning as this mistake cannot be caught at
> compile-time. We could remove the assignment operators, but this seems overly
> restrictive. We could also guard (via {{CHECK}}) the assignment operator
> after a {{get()}} operation, but of course, we're also preventing valid
> {{Try}} usage if we go this route. The best path may simply be to leave the
> assignment operators as is (many callers already make copies).
> We can also add C++11 support for move to pilfer the {{Try}}, to avoid copies
> in the caller entirely:
> {code}
> T&& move() const { ... } // After a move(), we must guard Try operations.
> {code}
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