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Re: [std-proposals] Dummy names for dummy objects

From: Arthur O'Dwyer <arthur.j.odwyer_at_[hidden]>
Date: Thu, 29 Jun 2023 12:17:23 -0400
On Thu, Jun 29, 2023 at 12:01 PM Harald Achitz <harald_at_[hidden]> wrote:

> > Use a cast to (void) to suppress nodiscardness.
> Will not pass a code review, for reason
I don't think you understand the status quo. I wasn't trying to express
advice that "Everyone should suppress nodiscardness at every turn." I was
simply expressing the actual fact that, *if* you want to suppress
nodiscardness, *then* you should use (void). (Or a project-specific macro
that expands to something like that.)
Obviously if your project has a coding guideline that states "Thou shalt
not suppress nodiscardness," then, corollary, thou shalt not use (void)
casts, either. (And this is great, because `(void)` is easily greppable.
Analogously, many projects state "Thou shalt not use raw owning pointers,"
corollary, thou shalt not use `new T` either; and people grep for `new` and
`delete` to verify that.)

For more on the messy state of [[nodiscard]]-suppression, see

If auto _ silences nodiscard warnings,
(It uses the result, so yes, it causes any warnings triggered by non-use
not to be emitted. This isn't what I mean by "suppression," though.)

> I can guarantee you, it will land on the list of features not to use in
> some projects, and it will be a point of discussion if / when we move to
> new standard version.

You still seem to be operating under the misapprehension that a programmer
might write either
    auto x = f();
    auto _ = f();
when what they actually meant to write was
and then *you would let that mistake through code review*. My advice to you
(both) is: Don't.
Furthermore, if you have a rule that "Thou shalt never ignore the result of
a [[nodiscard]] function," then you should actually be code-reviewing to
make sure that results of [[nodiscard]] functions are always used. If,
during code review, you see someone writing
    [[nodiscard]] int f();
    (void)f(); // X
    auto x = f(); (void)x; // X
    [[maybe_unused]] auto x = f(); // X
    std::ignore = std::make_tuple(f()); // X
    []{}(f()); // X
etc. etc., you should flag the lines marked `X` in code review and tell
them, "Hey, we have a rule here that you're *never* supposed to suppress
[[nodiscard]]ness! Go fix this code!"
Complaining about the C++26 semantics of `_` doesn't seem productive to
that end at all.



Received on 2023-06-29 16:17:38