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When implementing test code for N3794, I needed a function that creates a
chain of operator[] calls. Maybe we can do it for the Standard with
versions of the operator-calling function object classes, but with []. And
throw in () for the heck of it.

In section 20.10 [function.objects], add a set of declarations in paragraph
2, after the declarations for 20.10.7:

// 20.10.X, postfix operations:
template <class T = void> struct call;
template <class T = void> struct subscript;
template <> struct call<void>;
template <> struct subscript<void>;

Note that the non-specialized case is never defined, since there is no
legacy.

Add a new section after 20.10.7 [bitwise.operations]:

20.10.X [postfix.operations]

*-1-* The library provides function object classes for some of the postfix
operators in the language (5.2.1, 5.2.2).

template <> struct call<void> {
    template <class T, class... U>
    constexpr
    decltype(auto) operator()(T&& t, U&&... u) const noexcept(auto);

    typedef *unspecified *is_transparent;
};

*-2-* operator() returns std::forward<T>(t)( std::forward<U>(u)... ).

template <> struct subscript<void> {
    template <class T, class U>
    constexpr
    decltype(auto) operator()(T&& t, U&& u) const noexcept(auto);

    template <class T, class U, class V, class... W>
    constexpr
    decltype(auto) operator()(T&& t, U&& u, V&& v, W&&... w) const noexcept(
auto);

    typedef *unspecified *is_transparent;
};

*-3-* The first operator() returns std::forward<T>(t)[ std::forward<U>(u) ].
The second operator() returns operator()( std::forward<T>(t)[
std::forward<U>(u) ], std::forward<V>(v), std::forward<W>(w)... ).


Strictly, subscript<void> should only have the first operator. I'm not sure
whether we should create a new function (object) template (and a new name)
for a chain of subscript calls, or just reuse what we got. Yes, I know that
"noexcept( auto )" isn't legal (yet).

Are the names OK? Is "call" too generic?

Why don't the current operator-mirroring function object templates have
constexpr or noexcept indicators? Someone just forgot?

Daryle W.

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<div dir=3D"ltr">When implementing test code for N3794, I needed a function=
 that creates a chain of <font face=3D"courier new, monospace">operator[]</=
font> calls. Maybe we can do it for the Standard with versions of the opera=
tor-calling function object classes, but with []. And throw in () for the h=
eck of it.<div><br></div><div>In section 20.10 [function.objects], add a se=
t of declarations in paragraph 2, after the declarations for 20.10.7:</div>=
<div><br></div><div class=3D"prettyprint" style=3D"background-color: rgb(25=
0, 250, 250); border: 1px solid rgb(187, 187, 187); word-wrap: break-word;"=
><code class=3D"prettyprint"><div class=3D"subprettyprint"><span style=3D"c=
olor: #800;" class=3D"styled-by-prettify">// 20.10.X, postfix operations:</=
span><span style=3D"color: #000;" class=3D"styled-by-prettify"><br></span><=
span style=3D"color: #008;" class=3D"styled-by-prettify">template</span><sp=
an style=3D"color: #000;" class=3D"styled-by-prettify"> </span><span style=
=3D"color: #660;" class=3D"styled-by-prettify">&lt;</span><span style=3D"co=
lor: #008;" class=3D"styled-by-prettify">class</span><span style=3D"color: =
#000;" class=3D"styled-by-prettify"> T </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 style=3D"color: #008;" class=3D"style=
d-by-prettify">void</span><span style=3D"color: #660;" class=3D"styled-by-p=
rettify">&gt;</span><span style=3D"color: #000;" class=3D"styled-by-prettif=
y"> </span><span style=3D"color: #008;" class=3D"styled-by-prettify">struct=
</span><span style=3D"color: #000;" class=3D"styled-by-prettify"> call</spa=
n><span style=3D"color: #660;" class=3D"styled-by-prettify">;</span><span s=
tyle=3D"color: #000;" class=3D"styled-by-prettify"><br></span><span style=
=3D"color: #008;" class=3D"styled-by-prettify">template</span><span style=
=3D"color: #000;" class=3D"styled-by-prettify"> </span><span style=3D"color=
: #660;" class=3D"styled-by-prettify">&lt;</span><span style=3D"color: #008=
;" class=3D"styled-by-prettify">class</span><span style=3D"color: #000;" cl=
ass=3D"styled-by-prettify"> T </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 style=3D"color: #008;" class=3D"styled-by-pretti=
fy">void</span><span style=3D"color: #660;" class=3D"styled-by-prettify">&g=
t;</span><span style=3D"color: #000;" class=3D"styled-by-prettify"> </span>=
<span style=3D"color: #008;" class=3D"styled-by-prettify">struct</span><spa=
n style=3D"color: #000;" class=3D"styled-by-prettify"> subscript</span><spa=
n 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"co=
lor: #008;" class=3D"styled-by-prettify">template</span><span style=3D"colo=
r: #000;" class=3D"styled-by-prettify"> </span><span style=3D"color: #660;"=
 class=3D"styled-by-prettify">&lt;&gt;</span><span style=3D"color: #000;" c=
lass=3D"styled-by-prettify"> </span><span style=3D"color: #008;" class=3D"s=
tyled-by-prettify">struct</span><span style=3D"color: #000;" class=3D"style=
d-by-prettify"> call</span><span style=3D"color: #080;" class=3D"styled-by-=
prettify">&lt;void&gt;</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></span><span style=3D"color: #008;" class=3D"styled-by-prettify">tem=
plate</span><span style=3D"color: #000;" class=3D"styled-by-prettify"> </sp=
an><span style=3D"color: #660;" class=3D"styled-by-prettify">&lt;&gt;</span=
><span style=3D"color: #000;" class=3D"styled-by-prettify"> </span><span st=
yle=3D"color: #008;" class=3D"styled-by-prettify">struct</span><span style=
=3D"color: #000;" class=3D"styled-by-prettify"> subscript</span><span style=
=3D"color: #080;" class=3D"styled-by-prettify">&lt;void&gt;</span><span sty=
le=3D"color: #660;" class=3D"styled-by-prettify">;</span><span style=3D"col=
or: #000;" class=3D"styled-by-prettify"><br></span></div></code></div><div>=
<br></div><div>Note that the non-specialized case is never defined, since t=
here is no legacy.</div><div><br></div><div>Add a new section after 20.10.7=
 [bitwise.operations]:</div><div><br></div><blockquote style=3D"margin: 0 0=
 0 40px; border: none; padding: 0px;"><div><font size=3D"4">20.10.X [postfi=
x.operations]</font></div><div><br></div><div><b>-1-</b> The library provid=
es function object classes for some of the postfix operators in the languag=
e (5.2.1, 5.2.2).</div><div><br></div><div class=3D"prettyprint" style=3D"b=
ackground-color: rgb(250, 250, 250); border: 1px solid rgb(187, 187, 187); =
word-wrap: break-word;"><code class=3D"prettyprint"><div class=3D"subpretty=
print"><span style=3D"color: #008;" class=3D"styled-by-prettify">template</=
span><span style=3D"color: #000;" class=3D"styled-by-prettify"> </span><spa=
n style=3D"color: #660;" class=3D"styled-by-prettify">&lt;&gt;</span><span =
style=3D"color: #000;" class=3D"styled-by-prettify"> </span><span style=3D"=
color: #008;" class=3D"styled-by-prettify">struct</span><span style=3D"colo=
r: #000;" class=3D"styled-by-prettify"> call</span><span style=3D"color: #0=
80;" class=3D"styled-by-prettify">&lt;void&gt;</span><span style=3D"color: =
#000;" class=3D"styled-by-prettify"> </span><span style=3D"color: #660;" cl=
ass=3D"styled-by-prettify">{</span><span style=3D"color: #000;" class=3D"st=
yled-by-prettify"><br>&nbsp; &nbsp; </span><span style=3D"color: #008;" cla=
ss=3D"styled-by-prettify">template</span><span style=3D"color: #000;" class=
=3D"styled-by-prettify"> </span><span style=3D"color: #660;" class=3D"style=
d-by-prettify">&lt;</span><span style=3D"color: #008;" class=3D"styled-by-p=
rettify">class</span><span style=3D"color: #000;" class=3D"styled-by-pretti=
fy"> T</span><span style=3D"color: #660;" class=3D"styled-by-prettify">,</s=
pan><span style=3D"color: #000;" class=3D"styled-by-prettify"> </span><span=
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e=3D"color: #660;" class=3D"styled-by-prettify">...</span><span style=3D"co=
lor: #000;" class=3D"styled-by-prettify"> U</span><span style=3D"color: #66=
0;" class=3D"styled-by-prettify">&gt;</span><span style=3D"color: #000;" cl=
ass=3D"styled-by-prettify"><br>&nbsp; &nbsp; </span><span style=3D"color: #=
008;" class=3D"styled-by-prettify">constexpr</span><span style=3D"color: #0=
00;" class=3D"styled-by-prettify"><br>&nbsp; &nbsp; </span><span style=3D"c=
olor: #008;" class=3D"styled-by-prettify">decltype</span><span style=3D"col=
or: #660;" class=3D"styled-by-prettify">(</span><span style=3D"color: #008;=
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s=3D"styled-by-prettify">)</span><span style=3D"color: #000;" class=3D"styl=
ed-by-prettify"> </span><span style=3D"color: #008;" class=3D"styled-by-pre=
ttify">operator</span><span style=3D"color: #660;" class=3D"styled-by-prett=
ify">()(</span><span style=3D"color: #000;" class=3D"styled-by-prettify">T<=
/span><span style=3D"color: #660;" class=3D"styled-by-prettify">&amp;&amp;<=
/span><span style=3D"color: #000;" class=3D"styled-by-prettify"> t</span><s=
pan style=3D"color: #660;" class=3D"styled-by-prettify">,</span><span style=
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r: #660;" class=3D"styled-by-prettify">&amp;&amp;...</span><span style=3D"c=
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60;" class=3D"styled-by-prettify">)</span><span style=3D"color: #000;" clas=
s=3D"styled-by-prettify"> </span><span style=3D"color: #008;" class=3D"styl=
ed-by-prettify">const</span><span style=3D"color: #000;" class=3D"styled-by=
-prettify"> noexcept</span><span style=3D"color: #660;" class=3D"styled-by-=
prettify">(</span><font color=3D"#000000"><span style=3D"color: #008;" clas=
s=3D"styled-by-prettify">auto</span></font><span style=3D"color: #660;" cla=
ss=3D"styled-by-prettify">);</span><span style=3D"color: #000;" class=3D"st=
yled-by-prettify"><br><br>&nbsp; &nbsp; </span><span style=3D"color: #008;"=
 class=3D"styled-by-prettify">typedef</span><span style=3D"color: #000;" cl=
ass=3D"styled-by-prettify"> </span><i><span style=3D"color: #000;" class=3D=
"styled-by-prettify">unspecified </span></i><span style=3D"color: #000;" cl=
ass=3D"styled-by-prettify">is_transparent</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: #660;" class=3D"st=
yled-by-prettify">};</span><span style=3D"color: #000;" class=3D"styled-by-=
prettify"><br></span></div></code></div><div><br><b>-2-</b> <font face=3D"c=
ourier new, monospace">operator()</font> returns <font face=3D"courier new,=
 monospace">std::forward&lt;T&gt;(t)( std::forward&lt;U&gt;(u)... )</font>.=
<br></div><div><br></div><div class=3D"prettyprint" style=3D"background-col=
or: rgb(250, 250, 250); border: 1px solid rgb(187, 187, 187); word-wrap: br=
eak-word;"><code class=3D"prettyprint"><div class=3D"subprettyprint"><span =
style=3D"color: #008;" class=3D"styled-by-prettify">template</span><span st=
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lor: #660;" class=3D"styled-by-prettify">&lt;&gt;</span><span style=3D"colo=
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ss=3D"styled-by-prettify"> subscript</span><span style=3D"color: #080;" cla=
ss=3D"styled-by-prettify">&lt;void&gt;</span><span style=3D"color: #000;" c=
lass=3D"styled-by-prettify"> </span><span style=3D"color: #660;" class=3D"s=
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prettify"><br>&nbsp; &nbsp; </span><span style=3D"color: #008;" class=3D"st=
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an style=3D"color: #660;" class=3D"styled-by-prettify">...</span><span styl=
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: #008;" class=3D"styled-by-prettify">auto</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: #008;" class=3D"style=
d-by-prettify">operator</span><span style=3D"color: #660;" class=3D"styled-=
by-prettify">()(</span><span style=3D"color: #000;" class=3D"styled-by-pret=
tify">T</span><span style=3D"color: #660;" class=3D"styled-by-prettify">&am=
p;&amp;</span><span style=3D"color: #000;" class=3D"styled-by-prettify"> t<=
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an style=3D"color: #000;" class=3D"styled-by-prettify"> U</span><span style=
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n><span style=3D"color: #000;" class=3D"styled-by-prettify"> </span><span s=
tyle=3D"color: #008;" class=3D"styled-by-prettify">const</span><span style=
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=3D"color: #660;" class=3D"styled-by-prettify">(</span><span style=3D"color=
: #008;" class=3D"styled-by-prettify">auto</span><span style=3D"color: #660=
;" class=3D"styled-by-prettify">);</span><span style=3D"color: #000;" class=
=3D"styled-by-prettify"><br><br>&nbsp; &nbsp; </span><span style=3D"color: =
#008;" class=3D"styled-by-prettify">typedef</span><span style=3D"color: #00=
0;" class=3D"styled-by-prettify"> </span><i><span style=3D"color: #000;" cl=
ass=3D"styled-by-prettify">unspecified </span></i><span style=3D"color: #00=
0;" class=3D"styled-by-prettify">is_transparent</span><span style=3D"color:=
 #660;" class=3D"styled-by-prettify">;</span><span style=3D"color: #000;" c=
lass=3D"styled-by-prettify"><br></span><span style=3D"color: #660;" class=
=3D"styled-by-prettify">};</span><span style=3D"color: #000;" class=3D"styl=
ed-by-prettify"><br></span></div></code></div><div><br><b>-3-</b> The first=
 <font face=3D"courier new, monospace">operator()</font> returns <font face=
=3D"courier new, monospace">std::forward&lt;T&gt;(t)[ std::forward&lt;U&gt;=
(u) ]</font>. The second <font face=3D"courier new, monospace">operator()</=
font> returns <font face=3D"courier new, monospace">operator()( std::forwar=
d&lt;T&gt;(t)[ std::forward&lt;U&gt;(u) ], std::forward&lt;V&gt;(v), std::f=
orward&lt;W&gt;(w)... )</font>.<br></div></blockquote><div><br></div><div>S=
trictly, <font face=3D"courier new, monospace">subscript&lt;void&gt;</font>=
 should only have the first operator. I'm not sure whether we should create=
 a new function (object) template (and a new name) for a chain of subscript=
 calls, or just reuse what we got. Yes, I know that "<font face=3D"courier =
new, monospace">noexcept( auto )</font>" isn't legal (yet).</div><div><br><=
/div><div>Are the names OK? Is "<font face=3D"courier new, monospace">call<=
/font>" too generic?</div><div><br></div><div>Why don't the current operato=
r-mirroring function object templates have <font face=3D"courier new, monos=
pace">constexpr</font>&nbsp;or <font face=3D"courier new, monospace">noexce=
pt</font> indicators? Someone just forgot?</div><div><br></div><div>Daryle =
W.</div><div><br></div></div>

<p></p>

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