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I'd like to propose a simple, but very useful utility class for the
standard library: std::enum.

All it does is take a template parameter, which would be an enum type.

It would then allow you to access the individual elements of that enum, in
order of declaration, using a nearly identical interface as std::array<>
(i.e either through enumerators, or operator[]).

E.g:

#include <iostream>
#include <enum>
#include <algorithm>


enum Color { Red = 1, Green = 2, Blue = 23 };


int main()
{
   auto e = std::enum<Color>();
   for( auto v: e)
   {
     std::cout << "Elem: " << v << "\n";
   }
   std::cout << "Size: " << e.size() << "\n";
   std::cout << "Largest: " << std::max_element(e.begin(), e.end()) << "\n";
   return 0;
}

Output:
Elem: 1
Elem: 2
Elem: 23
Size: 3
Largest: 23

I assume that this would have to take some form of a help from the
compiler, similar to how std::underlying_type is implemented. However, this
would obviate the current set of hacks that either require macros, special
class constructions, or other inconvenient forms.

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<div dir=3D"ltr">I&#39;d like to propose a simple, but very useful utility =
class for the standard library: std::enum. =C2=A0<div><br></div><div>All it=
 does is take a template parameter, which would be an enum type.</div><div>=
<br></div><div>It would then allow you to access the individual elements of=
 that enum, in order of declaration, using a nearly identical interface as =
std::array&lt;&gt; (i.e either through enumerators, or operator[]).</div><d=
iv><div><br></div><div>E.g:=C2=A0</div><div><br></div><div class=3D"prettyp=
rint" style=3D"background-color: rgb(250, 250, 250); border-color: rgb(187,=
 187, 187); border-style: solid; border-width: 1px; word-wrap: break-word;"=
><code class=3D"prettyprint"><div class=3D"subprettyprint"><span style=3D"c=
olor: #800;" class=3D"styled-by-prettify">#include</span><span style=3D"col=
or: #000;" class=3D"styled-by-prettify"> </span><span style=3D"color: #080;=
" class=3D"styled-by-prettify">&lt;iostream&gt;</span><span style=3D"color:=
 #000;" class=3D"styled-by-prettify"><br></span><span style=3D"color: #800;=
" class=3D"styled-by-prettify">#include</span><span style=3D"color: #000;" =
class=3D"styled-by-prettify"> </span><span style=3D"color: #080;" class=3D"=
styled-by-prettify">&lt;enum&gt;</span><span style=3D"color: #000;" class=
=3D"styled-by-prettify"><br></span><span style=3D"color: #800;" class=3D"st=
yled-by-prettify">#include</span><span style=3D"color: #000;" class=3D"styl=
ed-by-prettify"> </span><span style=3D"color: #080;" class=3D"styled-by-pre=
ttify">&lt;algorithm&gt;</span><span style=3D"color: #000;" class=3D"styled=
-by-prettify"><br><br><br></span><span style=3D"color: #008;" class=3D"styl=
ed-by-prettify">enum</span><span style=3D"color: #000;" class=3D"styled-by-=
prettify"> </span><span style=3D"color: #606;" class=3D"styled-by-prettify"=
>Color</span><span style=3D"color: #000;" class=3D"styled-by-prettify"> </s=
pan><span style=3D"color: #660;" class=3D"styled-by-prettify">{</span><span=
 style=3D"color: #000;" class=3D"styled-by-prettify"> </span><span style=3D=
"color: #606;" class=3D"styled-by-prettify">Red</span><span style=3D"color:=
 #000;" class=3D"styled-by-prettify"> </span><span style=3D"color: #660;" c=
lass=3D"styled-by-prettify">=3D</span><span style=3D"color: #000;" class=3D=
"styled-by-prettify"> </span><span style=3D"color: #066;" class=3D"styled-b=
y-prettify">1</span><span style=3D"color: #660;" class=3D"styled-by-prettif=
y">,</span><span style=3D"color: #000;" class=3D"styled-by-prettify"> </spa=
n><span style=3D"color: #606;" class=3D"styled-by-prettify">Green</span><sp=
an style=3D"color: #000;" class=3D"styled-by-prettify"> </span><span style=
=3D"color: #660;" class=3D"styled-by-prettify">=3D</span><span style=3D"col=
or: #000;" class=3D"styled-by-prettify"> </span><span style=3D"color: #066;=
" class=3D"styled-by-prettify">2</span><span style=3D"color: #660;" class=
=3D"styled-by-prettify">,</span><span style=3D"color: #000;" class=3D"style=
d-by-prettify"> </span><span style=3D"color: #606;" class=3D"styled-by-pret=
tify">Blue</span><span style=3D"color: #000;" 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"styled-by-prettify"> </span><span st=
yle=3D"color: #066;" class=3D"styled-by-prettify">23</span><span style=3D"c=
olor: #000;" class=3D"styled-by-prettify"> </span><span style=3D"color: #66=
0;" class=3D"styled-by-prettify">};</span><span style=3D"color: #000;" clas=
s=3D"styled-by-prettify"><br><br><br></span><span style=3D"color: #008;" cl=
ass=3D"styled-by-prettify">int</span><span style=3D"color: #000;" class=3D"=
styled-by-prettify"> main</span><span style=3D"color: #660;" class=3D"style=
d-by-prettify">()</span><span style=3D"color: #000;" class=3D"styled-by-pre=
ttify"><br></span><span style=3D"color: #660;" class=3D"styled-by-prettify"=
>{</span><span style=3D"color: #000;" class=3D"styled-by-prettify"><br>=C2=
=A0 =C2=A0</span><span style=3D"color: #008;" class=3D"styled-by-prettify">=
auto</span><span style=3D"color: #000;" class=3D"styled-by-prettify"> e </s=
pan><span style=3D"color: #660;" class=3D"styled-by-prettify">=3D</span><sp=
an style=3D"color: #000;" class=3D"styled-by-prettify"> std</span><span sty=
le=3D"color: #660;" class=3D"styled-by-prettify">::</span><span style=3D"co=
lor: #008;" class=3D"styled-by-prettify">enum</span><span style=3D"color: #=
660;" class=3D"styled-by-prettify">&lt;</span><span style=3D"color: #606;" =
class=3D"styled-by-prettify">Color</span><span style=3D"color: #660;" class=
=3D"styled-by-prettify">&gt;();</span><span style=3D"color: #000;" class=3D=
"styled-by-prettify"><br>=C2=A0 =C2=A0</span><span style=3D"color: #008;" c=
lass=3D"styled-by-prettify">for</span><span style=3D"color: #660;" class=3D=
"styled-by-prettify">(</span><span style=3D"color: #000;" class=3D"styled-b=
y-prettify"> </span><span style=3D"color: #008;" class=3D"styled-by-prettif=
y">auto</span><span style=3D"color: #000;" class=3D"styled-by-prettify"> v<=
/span><span style=3D"color: #660;" class=3D"styled-by-prettify">:</span><sp=
an style=3D"color: #000;" class=3D"styled-by-prettify"> e</span><span style=
=3D"color: #660;" class=3D"styled-by-prettify">)</span><span style=3D"color=
: #000;" class=3D"styled-by-prettify"><br>=C2=A0 =C2=A0</span><span style=
=3D"color: #660;" class=3D"styled-by-prettify">{</span><span style=3D"color=
: #000;" class=3D"styled-by-prettify"><br>=C2=A0 =C2=A0 =C2=A0std</span><sp=
an style=3D"color: #660;" class=3D"styled-by-prettify">::</span><span style=
=3D"color: #000;" class=3D"styled-by-prettify">cout </span><span style=3D"c=
olor: #660;" class=3D"styled-by-prettify">&lt;&lt;</span><span style=3D"col=
or: #000;" class=3D"styled-by-prettify"> </span><span style=3D"color: #080;=
" class=3D"styled-by-prettify">&quot;Elem: &quot;</span><span style=3D"colo=
r: #000;" class=3D"styled-by-prettify"> </span><span style=3D"color: #660;"=
 class=3D"styled-by-prettify">&lt;&lt;</span><span style=3D"color: #000;" c=
lass=3D"styled-by-prettify"> v </span><span style=3D"color: #660;" class=3D=
"styled-by-prettify">&lt;&lt;</span><span style=3D"color: #000;" class=3D"s=
tyled-by-prettify"> </span><span style=3D"color: #080;" class=3D"styled-by-=
prettify">&quot;\n&quot;</span><span style=3D"color: #660;" class=3D"styled=
-by-prettify">;</span><span style=3D"color: #000;" class=3D"styled-by-prett=
ify"><br>=C2=A0 =C2=A0</span><span style=3D"color: #660;" class=3D"styled-b=
y-prettify">}</span><span style=3D"color: #000;" class=3D"styled-by-prettif=
y"><br>=C2=A0 =C2=A0std</span><span style=3D"color: #660;" class=3D"styled-=
by-prettify">::</span><span style=3D"color: #000;" class=3D"styled-by-prett=
ify">cout </span><span style=3D"color: #660;" class=3D"styled-by-prettify">=
&lt;&lt;</span><span style=3D"color: #000;" class=3D"styled-by-prettify"> <=
/span><span style=3D"color: #080;" class=3D"styled-by-prettify">&quot;Size:=
 &quot;</span><span style=3D"color: #000;" class=3D"styled-by-prettify"> </=
span><span style=3D"color: #660;" class=3D"styled-by-prettify">&lt;&lt;</sp=
an><span style=3D"color: #000;" class=3D"styled-by-prettify"> e</span><span=
 style=3D"color: #660;" class=3D"styled-by-prettify">.</span><span style=3D=
"color: #000;" class=3D"styled-by-prettify">size</span><span style=3D"color=
: #660;" class=3D"styled-by-prettify">()</span><span style=3D"color: #000;"=
 class=3D"styled-by-prettify"> </span><span style=3D"color: #660;" class=3D=
"styled-by-prettify">&lt;&lt;</span><span style=3D"color: #000;" class=3D"s=
tyled-by-prettify"> </span><span style=3D"color: #080;" class=3D"styled-by-=
prettify">&quot;\n&quot;</span><span style=3D"color: #660;" class=3D"styled=
-by-prettify">;</span><span style=3D"color: #000;" class=3D"styled-by-prett=
ify"><br>=C2=A0 =C2=A0std</span><span style=3D"color: #660;" class=3D"style=
d-by-prettify">::</span><span style=3D"color: #000;" class=3D"styled-by-pre=
ttify">cout </span><span style=3D"color: #660;" class=3D"styled-by-prettify=
">&lt;&lt;</span><span style=3D"color: #000;" class=3D"styled-by-prettify">=
 </span><span style=3D"color: #080;" class=3D"styled-by-prettify">&quot;Lar=
gest: &quot;</span><span style=3D"color: #000;" class=3D"styled-by-prettify=
"> </span><span style=3D"color: #660;" class=3D"styled-by-prettify">&lt;&lt=
;</span><span style=3D"color: #000;" class=3D"styled-by-prettify"> std</spa=
n><span style=3D"color: #660;" class=3D"styled-by-prettify">::</span><span =
style=3D"color: #000;" class=3D"styled-by-prettify">max_element</span><span=
 style=3D"color: #660;" class=3D"styled-by-prettify">(</span><span style=3D=
"color: #000;" class=3D"styled-by-prettify">e</span><span style=3D"color: #=
660;" class=3D"styled-by-prettify">.</span><span style=3D"color: #008;" cla=
ss=3D"styled-by-prettify">begin</span><span style=3D"color: #660;" class=3D=
"styled-by-prettify">(),</span><span style=3D"color: #000;" class=3D"styled=
-by-prettify"> e</span><span style=3D"color: #660;" class=3D"styled-by-pret=
tify">.</span><span style=3D"color: #008;" class=3D"styled-by-prettify">end=
</span><span style=3D"color: #660;" class=3D"styled-by-prettify">())</span>=
<span style=3D"color: #000;" class=3D"styled-by-prettify"> </span><span sty=
le=3D"color: #660;" class=3D"styled-by-prettify">&lt;&lt;</span><span style=
=3D"color: #000;" class=3D"styled-by-prettify"> </span><span style=3D"color=
: #080;" class=3D"styled-by-prettify">&quot;\n&quot;</span><span style=3D"c=
olor: #660;" class=3D"styled-by-prettify">;</span><span style=3D"color: #00=
0;" class=3D"styled-by-prettify"><br>=C2=A0 =C2=A0</span><span style=3D"col=
or: #008;" class=3D"styled-by-prettify">return</span><span style=3D"color: =
#000;" class=3D"styled-by-prettify"> </span><span style=3D"color: #066;" cl=
ass=3D"styled-by-prettify">0</span><span style=3D"color: #660;" class=3D"st=
yled-by-prettify">;</span><span style=3D"color: #000;" class=3D"styled-by-p=
rettify"><br></span><span style=3D"color: #660;" class=3D"styled-by-prettif=
y">}</span></div></code></div><div><font face=3D"courier new, monospace"><b=
r></font></div><div><font face=3D"arial, sans-serif">Output:</font></div><d=
iv class=3D"prettyprint" style=3D"background-color: rgb(250, 250, 250); bor=
der-color: rgb(187, 187, 187); border-style: solid; border-width: 1px; word=
-wrap: break-word;"><code class=3D"prettyprint"><div class=3D"subprettyprin=
t"><span style=3D"color: #606;" class=3D"styled-by-prettify">Elem</span><sp=
an style=3D"color: #660;" class=3D"styled-by-prettify">:</span><span style=
=3D"color: #000;" class=3D"styled-by-prettify"> </span><span style=3D"color=
: #066;" class=3D"styled-by-prettify">1</span><span style=3D"color: #000;" =
class=3D"styled-by-prettify"><br></span><span style=3D"color: #606;" class=
=3D"styled-by-prettify">Elem</span><span style=3D"color: #660;" class=3D"st=
yled-by-prettify">:</span><span style=3D"color: #000;" class=3D"styled-by-p=
rettify"> </span><span style=3D"color: #066;" class=3D"styled-by-prettify">=
2</span><span style=3D"color: #000;" class=3D"styled-by-prettify"><br></spa=
n><span style=3D"color: #606;" class=3D"styled-by-prettify">Elem</span><spa=
n style=3D"color: #660;" class=3D"styled-by-prettify">:</span><span style=
=3D"color: #000;" class=3D"styled-by-prettify"> </span><span style=3D"color=
: #066;" class=3D"styled-by-prettify">23</span><span style=3D"color: #000;"=
 class=3D"styled-by-prettify"><br></span><span style=3D"color: #606;" class=
=3D"styled-by-prettify">Size</span><span style=3D"color: #660;" class=3D"st=
yled-by-prettify">:</span><span style=3D"color: #000;" class=3D"styled-by-p=
rettify"> </span><span style=3D"color: #066;" class=3D"styled-by-prettify">=
3</span><span style=3D"color: #000;" class=3D"styled-by-prettify"><br></spa=
n><span style=3D"color: #606;" class=3D"styled-by-prettify">Largest</span><=
span style=3D"color: #660;" class=3D"styled-by-prettify">:</span><span styl=
e=3D"color: #000;" class=3D"styled-by-prettify"> </span><span style=3D"colo=
r: #066;" class=3D"styled-by-prettify">23</span></div></code></div><div><fo=
nt face=3D"courier new, monospace"><br></font></div><div>I assume that this=
 would have to take some form of a help from the compiler, similar to how s=
td::underlying_type is implemented. However, this would obviate the current=
 set of hacks that either require macros, special class constructions, or o=
ther inconvenient forms.</div></div><div><br></div></div>

<p></p>

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.

On Tuesday, 20 June 2017 20:34:28 PDT Halfdan Ingvarsson wrote:
> I'd like to propose a simple, but very useful utility class for the
> standard library: std::enum.

You need to find a different name. We can't have a class whose name is a
reserved keyword.

> All it does is take a template parameter, which would be an enum type.
>
> It would then allow you to access the individual elements of that enum, in
> order of declaration, using a nearly identical interface as std::array<>
> (i.e either through enumerators, or operator[]).

You're asking for enum reflection. There are many proposals about that, both
restricted to enums as well as generic (reflection for everything). The
restricted proposals haven't gained much traction, so everything now depends
on the full reflection proposals being accepted.

--
Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org
   Software Architect - Intel Open Source Technology Center

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.

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I won't think it can be done with only add lib.
For the samething I would suggest enum class will have a static const=20
variable array.
so that you could write
const auto & e =3DColor.array




=E5=9C=A8 2017=E5=B9=B46=E6=9C=8821=E6=97=A5=E6=98=9F=E6=9C=9F=E4=B8=89 UTC=
+8=E4=B8=8A=E5=8D=8811:34:28=EF=BC=8CHalfdan Ingvarsson=E5=86=99=E9=81=93=
=EF=BC=9A
>
> I'd like to propose a simple, but very useful utility class for the=20
> standard library: std::enum. =20
>
> All it does is take a template parameter, which would be an enum type.
>
> It would then allow you to access the individual elements of that enum, i=
n=20
> order of declaration, using a nearly identical interface as std::array<>=
=20
> (i.e either through enumerators, or operator[]).
>
> E.g:=20
>
> #include <iostream>
> #include <enum>
> #include <algorithm>
>
>
> enum Color { Red =3D 1, Green =3D 2, Blue =3D 23 };
>
>
> int main()
> {
>    auto e =3D std::enum<Color>();
>    for( auto v: e)
>    {
>      std::cout << "Elem: " << v << "\n";
>    }
>    std::cout << "Size: " << e.size() << "\n";
>    std::cout << "Largest: " << std::max_element(e.begin(), e.end()) <<=20
> "\n";
>    return 0;
> }
>
> Output:
> Elem: 1
> Elem: 2
> Elem: 23
> Size: 3
> Largest: 23
>
> I assume that this would have to take some form of a help from the=20
> compiler, similar to how std::underlying_type is implemented. However, th=
is=20
> would obviate the current set of hacks that either require macros, specia=
l=20
> class constructions, or other inconvenient forms.
>
>

--=20
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..org/d/msgid/std-proposals/546143ae-5acd-4a0e-abde-4f712c51ca30%40isocpp.or=
g.

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<div dir=3D"ltr">I won&#39;t think it can be done with only add lib.<div>Fo=
r the samething I would suggest enum class will have a static const variabl=
e array.</div><div>so that you could write</div><div><div class=3D"prettypr=
int" style=3D"background-color: rgb(250, 250, 250); border-color: rgb(187, =
187, 187); border-style: solid; border-width: 1px; word-wrap: break-word;">=
<code class=3D"prettyprint"><div class=3D"subprettyprint"><font color=3D"#0=
00000"><span style=3D"color: #008;" class=3D"styled-by-prettify">const</spa=
n><span style=3D"color: #000;" class=3D"styled-by-prettify"> </span><span s=
tyle=3D"color: #008;" class=3D"styled-by-prettify">auto</span><span style=
=3D"color: #000;" class=3D"styled-by-prettify"> </span><span style=3D"color=
: #660;" class=3D"styled-by-prettify">&amp;</span><span style=3D"color: #00=
0;" class=3D"styled-by-prettify"> e </span><span style=3D"color: #660;" cla=
ss=3D"styled-by-prettify">=3D</span><span style=3D"color: #606;" class=3D"s=
tyled-by-prettify">Color</span><span style=3D"color: #660;" class=3D"styled=
-by-prettify">.</span><span style=3D"color: #000;" class=3D"styled-by-prett=
ify">array</span></font></div></code></div><br><br><div><br><br>=E5=9C=A8 2=
017=E5=B9=B46=E6=9C=8821=E6=97=A5=E6=98=9F=E6=9C=9F=E4=B8=89 UTC+8=E4=B8=8A=
=E5=8D=8811:34:28=EF=BC=8CHalfdan Ingvarsson=E5=86=99=E9=81=93=EF=BC=9A<blo=
ckquote class=3D"gmail_quote" style=3D"margin: 0;margin-left: 0.8ex;border-=
left: 1px #ccc solid;padding-left: 1ex;"><div dir=3D"ltr">I&#39;d like to p=
ropose a simple, but very useful utility class for the standard library: st=
d::enum. =C2=A0<div><br></div><div>All it does is take a template parameter=
, which would be an enum type.</div><div><br></div><div>It would then allow=
 you to access the individual elements of that enum, in order of declaratio=
n, using a nearly identical interface as std::array&lt;&gt; (i.e either thr=
ough enumerators, or operator[]).</div><div><div><br></div><div>E.g:=C2=A0<=
/div><div><br></div><div style=3D"background-color:rgb(250,250,250);border-=
color:rgb(187,187,187);border-style:solid;border-width:1px;word-wrap:break-=
word"><code><div><span style=3D"color:#800">#include</span><span style=3D"c=
olor:#000"> </span><span style=3D"color:#080">&lt;iostream&gt;</span><span =
style=3D"color:#000"><br></span><span style=3D"color:#800">#include</span><=
span style=3D"color:#000"> </span><span style=3D"color:#080">&lt;enum&gt;</=
span><span style=3D"color:#000"><br></span><span style=3D"color:#800">#incl=
ude</span><span style=3D"color:#000"> </span><span style=3D"color:#080">&lt=
;algorithm&gt;</span><span style=3D"color:#000"><br><br><br></span><span st=
yle=3D"color:#008">enum</span><span style=3D"color:#000"> </span><span styl=
e=3D"color:#606">Color</span><span style=3D"color:#000"> </span><span style=
=3D"color:#660">{</span><span style=3D"color:#000"> </span><span style=3D"c=
olor:#606">Red</span><span style=3D"color:#000"> </span><span style=3D"colo=
r:#660">=3D</span><span style=3D"color:#000"> </span><span style=3D"color:#=
066">1</span><span style=3D"color:#660">,</span><span style=3D"color:#000">=
 </span><span style=3D"color:#606">Green</span><span style=3D"color:#000"> =
</span><span style=3D"color:#660">=3D</span><span style=3D"color:#000"> </s=
pan><span style=3D"color:#066">2</span><span style=3D"color:#660">,</span><=
span style=3D"color:#000"> </span><span style=3D"color:#606">Blue</span><sp=
an style=3D"color:#000"> </span><span style=3D"color:#660">=3D</span><span =
style=3D"color:#000"> </span><span style=3D"color:#066">23</span><span styl=
e=3D"color:#000"> </span><span style=3D"color:#660">};</span><span style=3D=
"color:#000"><br><br><br></span><span style=3D"color:#008">int</span><span =
style=3D"color:#000"> main</span><span style=3D"color:#660">()</span><span =
style=3D"color:#000"><br></span><span style=3D"color:#660">{</span><span st=
yle=3D"color:#000"><br>=C2=A0 =C2=A0</span><span style=3D"color:#008">auto<=
/span><span style=3D"color:#000"> e </span><span style=3D"color:#660">=3D</=
span><span style=3D"color:#000"> std</span><span style=3D"color:#660">::</s=
pan><span style=3D"color:#008">enum</span><span style=3D"color:#660">&lt;</=
span><span style=3D"color:#606">Color</span><span style=3D"color:#660">&gt;=
();</span><span style=3D"color:#000"><br>=C2=A0 =C2=A0</span><span style=3D=
"color:#008">for</span><span style=3D"color:#660">(</span><span style=3D"co=
lor:#000"> </span><span style=3D"color:#008">auto</span><span style=3D"colo=
r:#000"> v</span><span style=3D"color:#660">:</span><span style=3D"color:#0=
00"> e</span><span style=3D"color:#660">)</span><span style=3D"color:#000">=
<br>=C2=A0 =C2=A0</span><span style=3D"color:#660">{</span><span style=3D"c=
olor:#000"><br>=C2=A0 =C2=A0 =C2=A0std</span><span style=3D"color:#660">::<=
/span><span style=3D"color:#000">cout </span><span style=3D"color:#660">&lt=
;&lt;</span><span style=3D"color:#000"> </span><span style=3D"color:#080">&=
quot;Elem: &quot;</span><span style=3D"color:#000"> </span><span style=3D"c=
olor:#660">&lt;&lt;</span><span style=3D"color:#000"> v </span><span style=
=3D"color:#660">&lt;&lt;</span><span style=3D"color:#000"> </span><span sty=
le=3D"color:#080">&quot;\n&quot;</span><span style=3D"color:#660">;</span><=
span style=3D"color:#000"><br>=C2=A0 =C2=A0</span><span style=3D"color:#660=
">}</span><span style=3D"color:#000"><br>=C2=A0 =C2=A0std</span><span style=
=3D"color:#660">::</span><span style=3D"color:#000">cout </span><span style=
=3D"color:#660">&lt;&lt;</span><span style=3D"color:#000"> </span><span sty=
le=3D"color:#080">&quot;Size: &quot;</span><span style=3D"color:#000"> </sp=
an><span style=3D"color:#660">&lt;&lt;</span><span style=3D"color:#000"> e<=
/span><span style=3D"color:#660">.</span><span style=3D"color:#000">size</s=
pan><span style=3D"color:#660">()</span><span style=3D"color:#000"> </span>=
<span style=3D"color:#660">&lt;&lt;</span><span style=3D"color:#000"> </spa=
n><span style=3D"color:#080">&quot;\n&quot;</span><span style=3D"color:#660=
">;</span><span style=3D"color:#000"><br>=C2=A0 =C2=A0std</span><span style=
=3D"color:#660">::</span><span style=3D"color:#000">cout </span><span style=
=3D"color:#660">&lt;&lt;</span><span style=3D"color:#000"> </span><span sty=
le=3D"color:#080">&quot;Largest: &quot;</span><span style=3D"color:#000"> <=
/span><span style=3D"color:#660">&lt;&lt;</span><span style=3D"color:#000">=
 std</span><span style=3D"color:#660">::</span><span style=3D"color:#000">m=
ax_element</span><span style=3D"color:#660">(</span><span style=3D"color:#0=
00">e</span><span style=3D"color:#660">.</span><span style=3D"color:#008">b=
egin</span><span style=3D"color:#660">(),</span><span style=3D"color:#000">=
 e</span><span style=3D"color:#660">.</span><span style=3D"color:#008">end<=
/span><span style=3D"color:#660">())</span><span style=3D"color:#000"> </sp=
an><span style=3D"color:#660">&lt;&lt;</span><span style=3D"color:#000"> </=
span><span style=3D"color:#080">&quot;\n&quot;</span><span style=3D"color:#=
660">;</span><span style=3D"color:#000"><br>=C2=A0 =C2=A0</span><span style=
=3D"color:#008">return</span><span style=3D"color:#000"> </span><span style=
=3D"color:#066">0</span><span style=3D"color:#660">;</span><span style=3D"c=
olor:#000"><br></span><span style=3D"color:#660">}</span></div></code></div=
><div><font face=3D"courier new, monospace"><br></font></div><div><font fac=
e=3D"arial, sans-serif">Output:</font></div><div style=3D"background-color:=
rgb(250,250,250);border-color:rgb(187,187,187);border-style:solid;border-wi=
dth:1px;word-wrap:break-word"><code><div><span style=3D"color:#606">Elem</s=
pan><span style=3D"color:#660">:</span><span style=3D"color:#000"> </span><=
span style=3D"color:#066">1</span><span style=3D"color:#000"><br></span><sp=
an style=3D"color:#606">Elem</span><span style=3D"color:#660">:</span><span=
 style=3D"color:#000"> </span><span style=3D"color:#066">2</span><span styl=
e=3D"color:#000"><br></span><span style=3D"color:#606">Elem</span><span sty=
le=3D"color:#660">:</span><span style=3D"color:#000"> </span><span style=3D=
"color:#066">23</span><span style=3D"color:#000"><br></span><span style=3D"=
color:#606">Size</span><span style=3D"color:#660">:</span><span style=3D"co=
lor:#000"> </span><span style=3D"color:#066">3</span><span style=3D"color:#=
000"><br></span><span style=3D"color:#606">Largest</span><span style=3D"col=
or:#660">:</span><span style=3D"color:#000"> </span><span style=3D"color:#0=
66">23</span></div></code></div><div><font face=3D"courier new, monospace">=
<br></font></div><div>I assume that this would have to take some form of a =
help from the compiler, similar to how std::underlying_type is implemented.=
 However, this would obviate the current set of hacks that either require m=
acros, special class constructions, or other inconvenient forms.</div></div=
><div><br></div></div></blockquote></div></div></div>

<p></p>

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On Wednesday, June 21, 2017 at 12:06:54 AM UTC-4, Thiago Macieira wrote:
>
> On Tuesday, 20 June 2017 20:34:28 PDT Halfdan Ingvarsson wrote:
> > I'd like to propose a simple, but very useful utility class for the
> > standard library: std::enum.
>
> You need to find a different name. We can't have a class whose name is a
> reserved keyword.
>

Er. Yes. std::enum_array. It got lost in the wash.


> You're asking for enum reflection. There are many proposals about that,
> both
> restricted to enums as well as generic (reflection for everything). The
> restricted proposals haven't gained much traction, so everything now
> depends
> on the full reflection proposals being accepted.
>

Indeed.

So far, the only proposal I've seen where I can easily enumerate an enum in
a for-each, is the one from Sutton and Sutter (P0590R0). The rest are a
form of a <foo>::get<I>() template, where, if the proposal doesn't include
it, one would be forced to write some variadic template magic to cover that
aspect.

However, the front-runner reflection proposals all rely on the existence of
concepts in the standard, which makes me think that we're nowhere near
anything resembling reflection for a long time indeed.

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<div dir=3D"ltr">On Wednesday, June 21, 2017 at 12:06:54 AM UTC-4, Thiago M=
acieira wrote:<blockquote class=3D"gmail_quote" style=3D"margin: 0;margin-l=
eft: 0.8ex;border-left: 1px #ccc solid;padding-left: 1ex;">On Tuesday, 20 J=
une 2017 20:34:28 PDT Halfdan Ingvarsson wrote:
<br>&gt; I&#39;d like to propose a simple, but very useful utility class fo=
r the
<br>&gt; standard library: std::enum.
<br>
<br>You need to find a different name. We can&#39;t have a class whose name=
 is a=20
<br>reserved keyword.
<br></blockquote><div><br></div><div>Er. Yes. std::enum_array. It got lost =
in the wash.</div><div>=C2=A0</div><blockquote class=3D"gmail_quote" style=
=3D"margin: 0;margin-left: 0.8ex;border-left: 1px #ccc solid;padding-left: =
1ex;">You&#39;re asking for enum reflection. There are many proposals about=
 that, both=20
<br>restricted to enums as well as generic (reflection for everything). The=
=20
<br>restricted proposals haven&#39;t gained much traction, so everything no=
w depends=20
<br>on the full reflection proposals being accepted.
<br></blockquote><div><br></div><div>Indeed.=C2=A0</div><div><br></div><div=
>So far, the only proposal I&#39;ve seen where I can easily enumerate an en=
um in a for-each, is the one from Sutton and Sutter (P0590R0). The rest are=
 a form of a &lt;foo&gt;::get&lt;I&gt;() template, where, if the proposal d=
oesn&#39;t include it, one would be forced to write some variadic template =
magic to cover that aspect.</div><div><br></div><div>However, the front-run=
ner reflection proposals all rely on the existence of concepts in the stand=
ard, which makes me think that we&#39;re nowhere near anything resembling r=
eflection for a long time indeed.</div></div>

<p></p>

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On Wednesday, June 21, 2017 at 12:12:44 AM UTC-4, wei zhang wrote:
>
> I won't think it can be done with only add lib.
> For the samething I would suggest enum class will have a static const
> variable array.
> so that you could write
> const auto & e =Color.array
>

That's why I mentioned that it would have to have some help from the
compiler.

For example, std::underlying_type, on clang and gcc, rely on an intrinsic
called __underlying_type(), which takes a type argument. In this case there
needs to be something like __enum_members(), which would be substituted by
an braced init list that contains the enum members at compile time.

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<div dir=3D"ltr"><br><br>On Wednesday, June 21, 2017 at 12:12:44 AM UTC-4, =
wei zhang wrote:<blockquote class=3D"gmail_quote" style=3D"margin: 0;margin=
-left: 0.8ex;border-left: 1px #ccc solid;padding-left: 1ex;"><div dir=3D"lt=
r">I won&#39;t think it can be done with only add lib.<div>For the samethin=
g I would suggest enum class will have a static const variable array.</div>=
<div>so that you could write</div><div><div style=3D"background-color:rgb(2=
50,250,250);border-color:rgb(187,187,187);border-style:solid;border-width:1=
px;word-wrap:break-word"><code><div><font color=3D"#000000"><span style=3D"=
color:#008">const</span><span style=3D"color:#000"> </span><span style=3D"c=
olor:#008">auto</span><span style=3D"color:#000"> </span><span style=3D"col=
or:#660">&amp;</span><span style=3D"color:#000"> e </span><span style=3D"co=
lor:#660">=3D</span><span style=3D"color:#606">Color</span><span style=3D"c=
olor:#660">.</span><span style=3D"color:#000">array</span></font></div></co=
de></div></div></div></blockquote><div><br></div><div>That&#39;s why I ment=
ioned that it would have to have some help from the compiler.</div><div><br=
></div><div>For example, std::underlying_type, on clang and gcc, rely on an=
 intrinsic called __underlying_type(), which takes a type argument. In this=
 case there needs to be something like __enum_members(), which would be sub=
stituted by an braced init list that contains the enum members at compile t=
ime.</div><div><br></div><style type=3D"text/css">
p, li { white-space: pre-wrap; }
</style>
</div>

<p></p>

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On Wednesday, 21 June 2017 05:34:29 PDT Halfdan Ingvarsson wrote:
> However, the front-runner reflection proposals all rely on the existence of
> concepts in the standard, which makes me think that we're nowhere near
> anything resembling reflection for a long time indeed.

No, we're not. But since the proposals for restricted reflection haven't gained
much traction, then it seems like we'll have to wait for the generic solution.

--
Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org
   Software Architect - Intel Open Source Technology Center

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Since the Issaquah meeting, reflection seems to be getting more and more
realistic. I think there's legitimate space for hope in the near (non-17)
future...

2017-06-21 10:17 GMT-04:00 Thiago Macieira <thiago@macieira.org>:

> On Wednesday, 21 June 2017 05:34:29 PDT Halfdan Ingvarsson wrote:
> > However, the front-runner reflection proposals all rely on the existence
> of
> > concepts in the standard, which makes me think that we're nowhere near
> > anything resembling reflection for a long time indeed.
>
> No, we're not. But since the proposals for restricted reflection haven't
> gained
> much traction, then it seems like we'll have to wait for the generic
> solution.
>
> --
> Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org
>    Software Architect - Intel Open Source Technology Center
>
> --
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> isocpp.org/d/msgid/std-proposals/2384155.IuquL1aeVr%40tjmaciei-mobl1.
>

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<div dir=3D"ltr">Since the Issaquah meeting, reflection seems to be getting=
 more and more realistic. I think there&#39;s legitimate space for hope in =
the near (non-17) future...<br></div><div class=3D"gmail_extra"><br><div cl=
ass=3D"gmail_quote">2017-06-21 10:17 GMT-04:00 Thiago Macieira <span dir=3D=
"ltr">&lt;<a href=3D"mailto:thiago@macieira.org" target=3D"_blank">thiago@m=
acieira.org</a>&gt;</span>:<br><blockquote class=3D"gmail_quote" style=3D"m=
argin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><span class=
=3D"">On Wednesday, 21 June 2017 05:34:29 PDT Halfdan Ingvarsson wrote:<br>
&gt; However, the front-runner reflection proposals all rely on the existen=
ce of<br>
&gt; concepts in the standard, which makes me think that we&#39;re nowhere =
near<br>
&gt; anything resembling reflection for a long time indeed.<br>
<br>
</span>No, we&#39;re not. But since the proposals for restricted reflection=
 haven&#39;t gained<br>
much traction, then it seems like we&#39;ll have to wait for the generic so=
lution.<br>
<span class=3D""><br>
--<br>
Thiago Macieira - thiago (AT) <a href=3D"http://macieira.info" rel=3D"noref=
errer" target=3D"_blank">macieira.info</a> - thiago (AT) <a href=3D"http://=
kde.org" rel=3D"noreferrer" target=3D"_blank">kde.org</a><br>
=C2=A0 =C2=A0Software Architect - Intel Open Source Technology Center<br>
<br>
</span><span class=3D"">--<br>
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</blockquote></div><br></div>

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On Wednesday, June 21, 2017 at 11:34:28 AM UTC+8, Halfdan Ingvarsson wrote:
>
> I'd like to propose a simple, but very useful utility class for the
> standard library: std::enum.
>
> All it does is take a template parameter, which would be an enum type.
>
> It would then allow you to access the individual elements of that enum, in
> order of declaration, using a nearly identical interface as std::array<>
> (i.e either through enumerators, or operator[]).
>
> Because this depends on new language features, I think the motivation in
converting a "enum" to an array is not explicit enough.

As a user to the enum, I usually care "the mapping between names and
values" more than "the order of declaration". Would it be more reasonable
to convert an enum to an initializer list? For example:

enum E { ZERO = 0, ONE = 1, TWO = 2 };
std::map<std::string, int> a = MAKE_MAP(E); // MALE_MAP(E) is equivalent to
{{"ZERO", 0}, {"ONE", 1}, {"TWO", 2}}

Still, I think there should be more motivation. As I can imagine, this
feature is helpful in debugging and exception information generation.

Mingxin Wang

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<div dir=3D"ltr">On Wednesday, June 21, 2017 at 11:34:28 AM UTC+8, Halfdan =
Ingvarsson wrote:<blockquote class=3D"gmail_quote" style=3D"margin: 0;margi=
n-left: 0.8ex;border-left: 1px #ccc solid;padding-left: 1ex;"><div dir=3D"l=
tr">I&#39;d like to propose a simple, but very useful utility class for the=
 standard library: std::enum. =C2=A0<div><br></div><div>All it does is take=
 a template parameter, which would be an enum type.</div><div><br></div><di=
v>It would then allow you to access the individual elements of that enum, i=
n order of declaration, using a nearly identical interface as std::array&lt=
;&gt; (i.e either through enumerators, or operator[]).</div><div><div><br><=
/div></div></div></blockquote><div>Because this depends on new language fea=
tures, I think the motivation in converting a &quot;enum&quot; to an array =
is not explicit enough.</div><div><br></div><div>As a user to the enum, I u=
sually care &quot;the mapping between names and values&quot; more than &quo=
t;the order of declaration&quot;. Would it be more reasonable to convert an=
 enum to an initializer list? For example:</div><div><br></div><div><div cl=
ass=3D"prettyprint" style=3D"border: 1px solid rgb(187, 187, 187); word-wra=
p: break-word; background-color: rgb(250, 250, 250);"><code class=3D"pretty=
print"><div class=3D"subprettyprint"><div class=3D"subprettyprint">enum E {=
 ZERO =3D 0, ONE =3D 1, TWO =3D 2 };</div><div class=3D"subprettyprint">std=
::map&lt;std::string, int&gt; a =3D MAKE_MAP(E); // MALE_MAP(E) is equivale=
nt to {{&quot;ZERO&quot;, 0}, {&quot;ONE&quot;, 1}, {&quot;TWO&quot;, 2}}</=
div></div></code></div><br>Still, I think there should be more motivation. =
As I can imagine, this feature is helpful in debugging and exception inform=
ation generation.</div><div><br></div><div>Mingxin Wang</div></div>

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40isocpp.org?utm_medium=3Demail&utm_source=3Dfooter">https://groups.google.=
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%40isocpp.org</a>.<br />

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