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Subject: Re: [std-proposals] Allow [[deprecated]] on call site to disable deprecated warning
From: Marcin Jaczewski (marcinjaczewski86_at_[hidden])
Date: 2021-02-07 07:55:11


niedz., 7 lut 2021 o 14:46 Avi Kivity via Std-Proposals
<std-proposals_at_[hidden]> napisał(a):
>
>
> On 07/02/2021 13.37, Andrey Semashev via Std-Proposals wrote:
> > On February 7, 2021 1:22:41 PM Avi Kivity via Std-Proposals
> > <std-proposals_at_[hidden]> wrote:
> >
> >> On 28/01/2021 13.34, Ville Voutilainen via Std-Proposals wrote:
> >>> On Thu, 28 Jan 2021 at 13:06, Dominic Fandrey via Std-Proposals
> >>> <std-proposals_at_[hidden]> wrote:
> >>>> I recently ran into this issue:
> >>>>
> >>>> 1. Marked a set of legacy methods [[deprecated]]
> >>>> 2. Unit tests no longer compile (we run -Wall -Werror of course)
> >>>>
> >>>> Of course I don't want to get rid of the unit tests before I get
> >>>> rid of the
> >>>> functions. So I was faced with two choices:
> >>>>
> >>>> 1. Create #ifdef #pragma soup for all 3 compilers that we use
> >>>> 2. Remove [[deprecated]]
> >>>>
> >>>> The #ifdef #pragma soup needs to be updated every time a compiler
> >>>> is added,
> >>>> and it bloats the code and makes unit tests more difficult to read.
> >>>> So I
> >>>> went for option 2. As long as I cannot ignore [[deprecated]] in a
> >>>> portable
> >>>> manner I cannot use it.
> >>>>
> >>>> So my suggestion is:
> >>>>
> >>>> ```
> >>>> [[deprecated("use: std::optional<std::size_t> size()")]]int
> >>>> size(std::size_t & size);
> >>>>
> >>>>
> >>>> bool test_size() {
> >>>> std::size_t s{0};
> >>>> return 0 == [[deprecated]]size(s) && s != 0;
> >>>> }
> >>> Create your own MY_DEPRECATED macro, make it expand to actual
> >>> deprecation normally, but not in unit tests,
> >>> compile the unit tests with -DMY_SOMETHING that disables deprecations.
> >>> Or just add a #define into
> >>> your unit tests.
> >>
> >>
> >> Doesn't that break with modules?
> >>
> >>
> >> We should not be suggesting solutions that involve the preprocessor
> >> in 2021.
> >
> > I don't think that preprocessor is deprecated or its proper use should
> > be judged or anything. A preprocessor based solution is fine if this
> > tool is best fit for the job.
> >
> >
> >
>
> It does not work with modules. If I have a module that has a
> [[deprecated]] declaration, no amount of preprocessor tricks in the
> importing code will affect that declaration.
>
>

But if you control implementation adding `MY_DEPRECATED` and you
control the build of all modules (aka `-D???` compiler switch) then
this will work.
Of course you can't affect macros of module from other module as this
was one of the main goals of the model proposal.
But this is not this case. Only problem would be that you will need to
make a clear build of all modules when you change flags of
compilation.


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