Or just do this instead:

int main(void)
{
    mutex m;
    m.lock();
}


Does exactly the same thing, saves on functions calls, don't have to write a function, don't need to add a language feature, don't have to abuse the language, it actually makes sense from what a mutex is, its shorter, concise, transparent, clear.

Some problems don't need solving because they were never problems to begin with.


-----Original Message-----
From: Std-Proposals <std-proposals-bounces_at_lists.isocpp.org> On Behalf Of Frederick Virchanza Gotham via Std-Proposals
Sent: Monday, May 20, 2024 10:25
To: std-proposals_at_[hidden]ocpp.org
Cc: Frederick Virchanza Gotham <cauldwell.thomas_at_gmail.com>
Subject: Re: [std-proposals] std::elide

On Mon, May 20, 2024 at 7:59 AM Frederick Virchanza Gotham wrote:
>
> Or here's another way of doing it:
> If an exception is thrown and propagates outside of the function,
> then all destructors are invoked in the regular order -- except for
> the destructor of the return object, which is invoked last.


Actually I just had another idea.

------ Step 1: Start off by writing the function you want

mutex Func(void)
{
    mutex m;
    m.lock();
    return m;
}

------ Step 2: Re-write the function to manipulate an std::optional, we'll call this function an "optifunc":

void Func(optional<mutex> &arg)
{
    arg.emplace();
    arg->lock();
}

------ Step 3: Tell the compiler to take your optifunc and convert it into a NRVO function

using Func2 = std::nrvo_from_optifunc(Func);

------ Step 4: Now just invoke Func2

int main(void)
{
    mutex m = Func2();
}
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