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From Benjamin Bannier <benjamin.bann...@mesosphere.io>
Subject Re: Review Request 68813: Added support for `Option<T&>` / `Option<const T&>`.
Date Sun, 23 Sep 2018 11:31:31 GMT

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https://reviews.apache.org/r/68813/#review208927
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I am not convinced we should add this. The alternative of using e.g., an `Option<T*>`
or `Option<T const*>` seems to not only produce correct behavior (even when wrapping
a ptr to `const`), but also caution users enough that noting here protects against dangling
references or performs any reference lifetime extension. While this seems redundant in the
case of `Option` where one could just return a `nullptr` for `None` values, such a pattern
would translate seemlessly to e.g., `Try` or `Result`, and the behavior of empty case could
be solved by documentation wherever we would return such a type. It would also avoid unusual
semantics around assignment or comparision, and would e.g., continue to support hashing (the
type proposed here does not support `hash`).

I'd suggest to drop this patch and instead use wrappers around pointers if we really want
to provide such behavior in lieu of e.g., `contains` checks and returning naked values.

- Benjamin Bannier


On Sept. 23, 2018, 3:09 a.m., Benjamin Mahler wrote:
> 
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> This is an automatically generated e-mail. To reply, visit:
> https://reviews.apache.org/r/68813/
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> 
> (Updated Sept. 23, 2018, 3:09 a.m.)
> 
> 
> Review request for mesos, Benjamin Bannier, Benno Evers, and Michael Park.
> 
> 
> Bugs: MESOS-9252
>     https://issues.apache.org/jira/browse/MESOS-9252
> 
> 
> Repository: mesos
> 
> 
> Description
> -------
> 
> This adds support for options of references. While this is still
> under debate for `std::optional`, there are some use cases in
> stout that can benefit from this:
> 
>   // None if the value is not found, otherwise a reference
>   // to the value.
>   Option<T&> t = hashmap.get("key");
> 
> Assignment and equality are deleted in order to avoid confusion
> around which of the 2 possible behaviors they provide (e.g. are
> the references being compared? or are the objects being referred
> to being compared?)
> 
> 
> Diffs
> -----
> 
>   3rdparty/stout/include/stout/option.hpp 8feed012a55fed6eab89c883958324f3345e46e9 
> 
> 
> Diff: https://reviews.apache.org/r/68813/diff/1/
> 
> 
> Testing
> -------
> 
> Test added in subsequent patch.
> 
> 
> Thanks,
> 
> Benjamin Mahler
> 
>


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