220 2124 <CAFk2RUZyZA0LLUNuVNcnibv+qBF69jMytWQL3tkp-Kp21oEU+A@mail.gmail.com> article
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From: Ville Voutilainen <ville.voutilainen@gmail.com>
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Subject: Re: optional<T>, one more value or two states
Date: Thu, 24 Jan 2013 15:38:21 +0200
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On 24 January 2013 15:25, Zhihao Yuan <lichray@gmail.com> wrote:
> My own point of view:
> If optional<T> is an extended type T, then:
> optional<int> x = 0;  // implicitly convertible
> optional<int>(3) == 3;  // since T is a sub-range of optional<T>
> optional<int>(nullopt) == optional<int>(nullopt);  // same extended value
> If optional<T> is a T with two states, then:
> optional<int> x(0);  // explicitly convertible
> optional<int>(3) == make_optional(3);  // since T is not "T with states"
> optional<int>(nullopt) != optional<int>(nullopt);  // meaningless states
> Comments wanted.

I initially thought implicit conversions from T to optional<T> are a bad idea.
I have since cured that problem in my head, there's no 'danger' involved in
it. boost::optional has such implicit conversions, and I see no reason
to do it differently for std::optional.

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