Topic: Treating qualified names as types
Author: Columbo <r.hl@gmx.net>
Date: Sun, 31 May 2015 06:24:02 -0700 (PDT)
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=C2=A714.6/5 'allows' to use dependent qualified names as types if they app=
ear=20
in certain contexts. E.g. in base-specifiers.
Can we extend this to other contexts in which using typename is currently=
=20
necessary but not actually removing ambiguities? Particularly,=20
alias-declarations? E.g..
template <typename T>
using eval =3D T::type;
I can't see how this breaks code, but I feel that it would make it more=20
readable.=20
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<div dir=3D"ltr">=C2=A714.6/5 'allows' to use dependent qualified names as =
types if they appear in certain contexts. E.g. in base-specifiers.<div>Can =
we extend this to other contexts in which using <font face=3D"courier new, =
monospace">typename</font> is currently necessary but not actually removing=
ambiguities? Particularly, alias-declarations? E.g..<br></div><div class=
=3D"prettyprint" style=3D"border: 1px solid rgb(187, 187, 187); word-wrap: =
break-word; background-color: rgb(250, 250, 250);"><code class=3D"prettypri=
nt"><div class=3D"subprettyprint"><span style=3D"color: #008;" class=3D"sty=
led-by-prettify">template</span><span style=3D"color: #000;" class=3D"style=
d-by-prettify"> </span><span style=3D"color: #660;" class=3D"styled-by-pret=
tify"><</span><span style=3D"color: #008;" class=3D"styled-by-prettify">=
typename</span><span style=3D"color: #000;" class=3D"styled-by-prettify"> T=
</span><span style=3D"color: #660;" class=3D"styled-by-prettify">></span=
><span style=3D"color: #000;" class=3D"styled-by-prettify"><br></span><span=
style=3D"color: #008;" class=3D"styled-by-prettify">using</span><span styl=
e=3D"color: #000;" class=3D"styled-by-prettify"> </span><span style=3D"colo=
r: #008;" class=3D"styled-by-prettify">eval</span><span style=3D"color: #00=
0;" class=3D"styled-by-prettify"> </span><span style=3D"color: #660;" class=
=3D"styled-by-prettify">=3D</span><span style=3D"color: #000;" class=3D"sty=
led-by-prettify"> T</span><span style=3D"color: #660;" class=3D"styled-by-p=
rettify">::</span><span style=3D"color: #000;" class=3D"styled-by-prettify"=
>type</span><span style=3D"color: #660;" class=3D"styled-by-prettify">;</sp=
an></div></code></div><div><br></div><div>I can't see how this breaks code,=
but I feel that it would make it more readable. </div></div>
<p></p>
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Author: Richard Smith <richard@metafoo.co.uk>
Date: Sun, 31 May 2015 12:46:42 -0700
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On Sun, May 31, 2015 at 6:24 AM, Columbo <r.hl@gmx.net> wrote:
> =C2=A714.6/5 'allows' to use dependent qualified names as types if they a=
ppear
> in certain contexts. E.g. in base-specifiers.
> Can we extend this to other contexts in which using typename is currently
> necessary but not actually removing ambiguities? Particularly,
> alias-declarations? E.g..
> template <typename T>
> using eval =3D T::type;
>
> I can't see how this breaks code, but I feel that it would make it more
> readable.
>
That is deliberately disallowed in order to allow the "using" syntax to be
extended to cover other kinds of entities in future revisions of the
standard. This was discussed in the papers introducing the
alias-declaration syntax.
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<div dir=3D"ltr"><div class=3D"gmail_extra"><div class=3D"gmail_quote">On S=
un, May 31, 2015 at 6:24 AM, Columbo <span dir=3D"ltr"><<a href=3D"mailt=
o:r.hl@gmx.net" target=3D"_blank">r.hl@gmx.net</a>></span> wrote:<br><bl=
ockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #=
ccc solid;padding-left:1ex"><div dir=3D"ltr">=C2=A714.6/5 'allows' =
to use dependent qualified names as types if they appear in certain context=
s. E.g. in base-specifiers.<div>Can we extend this to other contexts in whi=
ch using <font face=3D"courier new, monospace">typename</font> is currently=
necessary but not actually removing ambiguities? Particularly, alias-decla=
rations? E.g..<br></div><div style=3D"border:1px solid rgb(187,187,187);wor=
d-wrap:break-word;background-color:rgb(250,250,250)"><code><div><span style=
=3D"color:#008">template</span><span style=3D"color:#000"> </span><span sty=
le=3D"color:#660"><</span><span style=3D"color:#008">typename</span><spa=
n style=3D"color:#000"> T</span><span style=3D"color:#660">></span><span=
style=3D"color:#000"><br></span><span style=3D"color:#008">using</span><sp=
an style=3D"color:#000"> </span><span style=3D"color:#008">eval</span><span=
style=3D"color:#000"> </span><span style=3D"color:#660">=3D</span><span st=
yle=3D"color:#000"> T</span><span style=3D"color:#660">::</span><span style=
=3D"color:#000">type</span><span style=3D"color:#660">;</span></div></code>=
</div><div><br></div><div>I can't see how this breaks code, but I feel =
that it would make it more readable.=C2=A0</div></div></blockquote><div><br=
></div><div>That is deliberately disallowed in order to allow the "usi=
ng" syntax to be extended to cover other kinds of entities in future r=
evisions of the standard. This was discussed in the papers introducing the =
alias-declaration syntax.</div></div></div></div>
<p></p>
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