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Subject: Re: [std-proposals] Fixing some initialization gotchas
From: Matthew Woehlke (mwoehlke.floss_at_[hidden])
Date: 2019-08-23 11:40:43


On 23/08/2019 11.35, Ville Voutilainen via Std-Proposals wrote:
> On Fri, 23 Aug 2019 at 18:21, Maciej Cencora wrote:
>> I cannot pass multiple elements in that form now, but it was possible before in C++11.
>>
>> It is a simplification, because it avoids ambiguities, surprises, and removes corner cases.
>> Currently this one compiles:
>> auto x1 = { 1 };
>> auto x2 = { 1, 1 };
>> auto x3{ 1 };
>> auto x4{ 1, 1 };
>>
>> Currently only x1 and x2 has same type, x4 does not compile, x1 and x2 compiles only if you include initializer_list header.
>> And x1 type is different then x3.
>> This is complete bonkers!
>
> Indeed it is. But in order to get x3, some parties insisted on keeping
> x1/x2 working as they were, so that's the compromise we have.

Who actually *wanted* x3, and why?

>> With my proposal the only allow auto declaration would be in following form:
>> auto x = y;
>> which is unambiguous, has no corner cases, and works just as right now.
>
> Yeah, and then T a{x}; works but auto a{x} doesn't, so yeah, you do
> have corner cases.

I could live with that. IMHO, `auto a{x}` doesn't make sense; there is
no "obvious" rule how to determine what the type of `a` should be,
unlike just about every other instance where `auto` is used. Consider
that `{x}`, by itself, is a nonsense expression, If anything, I *could*
see it as an initializer list, but making it equivalent to `x` doesn't
make sense IMO.

-- 
Matthew

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