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Newsgroups: gmane.comp.lang.c++.isocpp.proposals
Subject: Re: optional<T>, one more value or two states
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W dniu czwartek, 24 stycznia 2013 14:25:49 UTC+1 u=BFytkownik Zhihao Yuan=
=20
napisa=B3:
>
> My own point of view:=20
>
> If optional<T> is an extended type T, then:=20
>
> optional<int> x =3D 0;  // implicitly convertible=20
> optional<int>(3) =3D=3D 3;  // since T is a sub-range of optional<T>=20
> optional<int>(nullopt) =3D=3D optional<int>(nullopt);  // same extended v=
alue=20
>
> If optional<T> is a T with two states, then:=20
>
> optional<int> x(0);  // explicitly convertible=20
> optional<int>(3) =3D=3D make_optional(3);  // since T is not "T with stat=
es"=20
> optional<int>(nullopt) !=3D optional<int>(nullopt);  // meaningless state=
s=20
>
> Comments wanted.=20
>

Terms "extended type" and "a type with two states" are very confusing for=
=20
me. I am not sure what you mean. Instead, if you asked -- in the spirit of=
=20
n2479 <http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2479.pdf>--=
 what the set of salient attributes of optional<T> is, the answer is easy.

The salient attributes are:

   1. The engaged/disengaged state
   2. If the optional object is engaged, the value of its 'contained value'=
..
  =20

--=20

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<br><br>W dniu czwartek, 24 stycznia 2013 14:25:49 UTC+1 u=BFytkownik Zhiha=
o Yuan napisa=B3:<blockquote class=3D"gmail_quote" style=3D"margin: 0;margi=
n-left: 0.8ex;border-left: 1px #ccc solid;padding-left: 1ex;">My own point =
of view:
<br>
<br>If optional&lt;T&gt; is an extended type T, then:
<br>
<br>optional&lt;int&gt; x =3D 0; &nbsp;// implicitly convertible
<br>optional&lt;int&gt;(3) =3D=3D 3; &nbsp;// since T is a sub-range of opt=
ional&lt;T&gt;
<br>optional&lt;int&gt;(nullopt) =3D=3D optional&lt;int&gt;(nullopt); &nbsp=
;// same extended value
<br>
<br>If optional&lt;T&gt; is a T with two states, then:
<br>
<br>optional&lt;int&gt; x(0); &nbsp;// explicitly convertible
<br>optional&lt;int&gt;(3) =3D=3D make_optional(3); &nbsp;// since T is not=
 "T with states"
<br>optional&lt;int&gt;(nullopt) !=3D optional&lt;int&gt;(nullopt); &nbsp;/=
/ meaningless states
<br>
<br>Comments wanted.
<br></blockquote><div><br>Terms "extended type" and "a type with two states=
" are very confusing for me. I am not sure what you mean. Instead, if you a=
sked -- in the spirit of <a href=3D"http://www.open-std.org/jtc1/sc22/wg21/=
docs/papers/2007/n2479.pdf ">n2479</a> -- what the set of salient attribute=
s of optional&lt;T&gt; is, the answer is easy.<br><br>The salient attribute=
s are:<br><ol><li>The engaged/disengaged state</li><li>If the optional obje=
ct is engaged, the value of its 'contained value'.<br></li></ol></div>

<p></p>

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&nbsp;<br />
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&nbsp;<br />
&nbsp;<br />

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