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Today, we can use as a template argument classes declared earlier.
Sometimes it can be useful to declare classes in the place of use - in
angle brackets of template instantiation. In particular, it would be useful
for a compact joining metainformation to object.

For example:

// some template class
template<class T>
class Foo
{
//...
};

// instantiation of template using named in-place declared structure
Foo< struct MetaInfo { const char* get_name() { return "foo1"; } } > foo1;

// instantiation of template using unnamed in-place declared structure
Foo< struct { const char* get_name() { return "foo2"; } } > foo2;


These in-place declared types (even named) are invisible outside template
instantiation; in fact, they are not do not need outside template
instantiation; in tempate Foo, they are accessible as template parameter "T"
..

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<div dir=3D"ltr">Today, we can use as a template argument classes declared =
earlier. Sometimes it can be useful to declare classes in the place of use =
- in angle brackets of template instantiation. In particular, it would be u=
seful for a compact joining metainformation to object.<div><br></div><div>F=
or example:</div><div><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"prettyprint"><div class=3D"subprettyprint"=
><span style=3D"color: #800;" class=3D"styled-by-prettify">// some template=
 class</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><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;" class=3D"styled-by-prettify"> T</span><span style=3D=
"color: #660;" class=3D"styled-by-prettify">&gt;</span><span style=3D"color=
: #000;" class=3D"styled-by-prettify"> <br></span><span style=3D"color: #00=
8;" class=3D"styled-by-prettify">class</span><span style=3D"color: #000;" c=
lass=3D"styled-by-prettify"> </span><span style=3D"color: #606;" class=3D"s=
tyled-by-prettify">Foo</span><span style=3D"color: #000;" class=3D"styled-b=
y-prettify"> <br></span><span style=3D"color: #660;" class=3D"styled-by-pre=
ttify">{</span><span style=3D"color: #000;" class=3D"styled-by-prettify"> &=
nbsp; &nbsp; &nbsp;<br></span><span style=3D"color: #800;" class=3D"styled-=
by-prettify">//...</span><span style=3D"color: #000;" class=3D"styled-by-pr=
ettify"><br></span><span style=3D"color: #660;" class=3D"styled-by-prettify=
">};</span><span style=3D"color: #000;" class=3D"styled-by-prettify"><br><b=
r></span><span style=3D"color: #800;" class=3D"styled-by-prettify">// insta=
ntiation of template using named in-place declared structure</span><span st=
yle=3D"color: #000;" class=3D"styled-by-prettify"><br></span><span style=3D=
"color: #606;" class=3D"styled-by-prettify">Foo</span><span style=3D"color:=
 #660;" class=3D"styled-by-prettify">&lt;</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"color: #000;" class=3D"=
styled-by-prettify"> </span><span style=3D"color: #606;" class=3D"styled-by=
-prettify">MetaInfo</span><span style=3D"color: #000;" class=3D"styled-by-p=
rettify"> </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"styled-by-prettify">const</span><span =
style=3D"color: #000;" class=3D"styled-by-prettify"> </span><span style=3D"=
color: #008;" class=3D"styled-by-prettify">char</span><span style=3D"color:=
 #660;" class=3D"styled-by-prettify">*</span><span style=3D"color: #000;" c=
lass=3D"styled-by-prettify"> get_name</span><span style=3D"color: #660;" cl=
ass=3D"styled-by-prettify">()</span><span style=3D"color: #000;" class=3D"s=
tyled-by-prettify"> </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"styled-by-prettify">return</=
span><span style=3D"color: #000;" class=3D"styled-by-prettify"> </span><spa=
n style=3D"color: #080;" class=3D"styled-by-prettify">"foo1"</span><span st=
yle=3D"color: #660;" class=3D"styled-by-prettify">;</span><span style=3D"co=
lor: #000;" class=3D"styled-by-prettify"> </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"style=
d-by-prettify">}</span><span style=3D"color: #000;" class=3D"styled-by-pret=
tify"> </span><span style=3D"color: #660;" class=3D"styled-by-prettify">&gt=
;</span><span style=3D"color: #000;" class=3D"styled-by-prettify"> foo1</sp=
an><span style=3D"color: #660;" class=3D"styled-by-prettify">;</span><span =
style=3D"color: #000;" class=3D"styled-by-prettify"><br><br></span><span st=
yle=3D"color: #800;" class=3D"styled-by-prettify">// instantiation of templ=
ate using unnamed in-place declared structure</span><span style=3D"color: #=
000;" class=3D"styled-by-prettify"><br></span><span style=3D"color: #606;" =
class=3D"styled-by-prettify">Foo</span><span style=3D"color: #660;" class=
=3D"styled-by-prettify">&lt;</span><span style=3D"color: #000;" class=3D"st=
yled-by-prettify"> </span><span style=3D"color: #008;" class=3D"styled-by-p=
rettify">struct</span><span style=3D"color: #000;" class=3D"styled-by-prett=
ify"> </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=
 style=3D"color: #008;" class=3D"styled-by-prettify">const</span><span styl=
e=3D"color: #000;" class=3D"styled-by-prettify"> </span><span style=3D"colo=
r: #008;" class=3D"styled-by-prettify">char</span><span style=3D"color: #66=
0;" class=3D"styled-by-prettify">*</span><span style=3D"color: #000;" class=
=3D"styled-by-prettify"> get_name</span><span style=3D"color: #660;" class=
=3D"styled-by-prettify">()</span><span style=3D"color: #000;" class=3D"styl=
ed-by-prettify"> </span><span style=3D"color: #660;" class=3D"styled-by-pre=
ttify">{</span><span style=3D"color: #000;" class=3D"styled-by-prettify"> <=
/span><span style=3D"color: #008;" class=3D"styled-by-prettify">return</spa=
n><span style=3D"color: #000;" class=3D"styled-by-prettify"> </span><span s=
tyle=3D"color: #080;" class=3D"styled-by-prettify">"foo2"</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">}</span><span style=3D"color: #000;" class=3D"=
styled-by-prettify"> </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">&gt;</s=
pan><span style=3D"color: #000;" class=3D"styled-by-prettify"> foo2</span><=
span style=3D"color: #660;" class=3D"styled-by-prettify">;</span><span styl=
e=3D"color: #000;" class=3D"styled-by-prettify"><br><br></span></div></code=
></div><div style=3D"orphans: 2; text-align: -webkit-auto; widows: 2;"><div=
 style=3D"color: rgb(0, 0, 0); font-family: Tahoma; font-size: medium; text=
-align: -webkit-auto;"><br></div><div style=3D"text-align: -webkit-auto;"><=
span style=3D"color: rgb(34, 34, 34); font-family: Arial, Helvetica, sans-s=
erif; font-size: 13px; orphans: auto; widows: auto;">These in-place declare=
d types (</span><span style=3D"text-align: -webkit-auto;">even named</span>=
<span style=3D"text-align: -webkit-auto; orphans: auto; widows: auto;">) ar=
e invisible outside template instantiation; in fact, they are not&nbsp;</sp=
an><span style=3D"text-align: -webkit-auto;">do not need outside&nbsp;</spa=
n><span style=3D"text-align: -webkit-auto; orphans: auto; widows: auto;">te=
mplate instantiation; in tempate Foo, they are accessible as template param=
eter&nbsp;</span><span style=3D"text-align: -webkit-auto; orphans: auto; wi=
dows: auto;">"T"</span><span style=3D"text-align: -webkit-auto; orphans: au=
to; widows: auto;">.</span></div><div style=3D"text-align: -webkit-auto;"><=
br></div></div></div>

<p></p>

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