blocks|key|4958754|text|呼叫树：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4958755|+WriteLog("apple,+",+"orange,+",+"mango");
+++++++->WriteLog("apple,+");
++++++++++++->+std::wcout+<<+"apple,+";
+++++++->WriteLog(+"orange,+",+"mango");
++++++++++++->WriteLog("orange,+");
+++++++++++++++++->+std::wcout+<<+"orange,+";
++++++++++++->WriteLog(+"mango");
+++++++++++++++++->+std::wcout+<<+"mango";
++++++++++++->std::wcout+<<+"\n**End**";
+++++++->std::wcout+<<+"\n**End**";|code-block|syntax|javascript|4958756|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

the call tree :

<pre><code> WriteLog("apple, ", "orange, ", "mango");
 -&gt;WriteLog("apple, ");
 -&gt; std::wcout &lt;&lt; "apple, ";
 -&gt;WriteLog( "orange, ", "mango");
 -&gt;WriteLog("orange, ");
 -&gt; std::wcout &lt;&lt; "orange, ";
 -&gt;WriteLog( "mango");
 -&gt; std::wcout &lt;&lt; "mango";
 -&gt;std::wcout &lt;&lt; "\n**End**";
 -&gt;std::wcout &lt;&lt; "\n**End**";
</code></pre>

blocks|key|4958781|text|完成对WriteLog(std::forward<Ts>(Vals)...);的递归调用后，它必须执行下一个语句。此函数被调用两次(一次用于"apple"，一次用于"orange")，因此编写了两次"**End**"打印输出。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4958782|对"mango"的最后一次递归调用直接进入第一个重载，因为包中只剩下一个参数。|4958783|entityMap^0|3|10|1Y|7|2A|8|2R|9|0|1|7|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]|$9|M|A|N|B|C]|$9|O|A|P|B|C]|$9|Q|A|R|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|I|$]]

When the recursive call to <code>WriteLog(std::forward&lt;Ts&gt;(Vals)...);</code> is finished, it has to execute the next statement. This function is called twice (once for <code>"apple"</code> and once for <code>"orange"</code>) and thus two print outs of <code>"**End**"</code> are written.

The last recursive call for <code>"mango"</code> goes straight to the first overload since there is only a single argument left in the pack.

blocks|key|944112|text|的调用打印**End**。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|944113|WriteLog("apple,+",+"orange,+",+"mango");+in+main|unordered-list-item|944114|WriteLog("orange,+",+"mango");+(带行WriteLog(std::forward<Ts>(Vals)...);)在WriteLog("apple,+",+"orange,+",+"mango")中|944115|entityMap^0|5|7|0|0|15|19|4|0|0|U|Y|10|20|14|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@$9|Q|A|R|B|C]|$9|S|A|T|B|C]]|D|@]|E|$]]|$1|I|3|J|5|H|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]|$9|Z|A|10|B|C]]|D|@]|E|$]]|$1|K|3|-4|5|6|7|11|8|@]|D|@]|E|$]]]|L|$]]

<code>**End**</code> is printed for the calls of

<ul>
<li><code>WriteLog("apple, ", "orange, ", "mango");</code> in <code>main</code></li>
<li><code>WriteLog("orange, ", "mango");</code> (with line <code>WriteLog(std::forward&lt;Ts&gt;(Vals)...);</code>) in <code>WriteLog("apple, ", "orange, ", "mango")</code></li>
</ul>

blocks|key|4958837|text|老实说，我已经写了4年的c%2B%2B11模板代码，我仍然很难记住如何匹配空的参数包.|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4958838|这个小技巧完全避免了递归模板的扩展：(编辑:重写以支持零参数和自动逗号分隔符插入)|4958839|#include+<iostream>

namespace+detail+{
++++struct+writer
++++{
++++++++template<class+T>
++++++++void+operator()(const+T&+t)+{
++++++++++++if+(_first)+{
++++++++++++++++_first+=+false;
++++++++++++}
++++++++++++else+{
++++++++++++++++std::cout+<<+",+";
++++++++++++}
++++++++++++std::cout+<<+t;
++++++++}

++++private:
++++++++bool+_first+=+true;
++++};

++++//+non-template+overload+to+catch+no-parameter+case
++++void+do_write(writer&&)
++++{

++++}

++++//+general+case.+Note+w+is+passed+by+r-value+reference
++++//+to+allow+the+caller+to+construct+it+in-place++++++++
++++template<typename+T,+typename...Ts>
++++void+do_write(writer&&+w,+const+T&+t,+Ts&&...ts)
++++{
++++++++w(t);
++++++++do_write(std::forward<writer>(w),+std::forward<Ts>(ts)...);
++++}


}

//+method+1+-+no+recursion
template<typename...+Ts>
void+WriteLog1(Ts&&...+Vals)+{
++++//+expand+one+call+for+each+parameter
++++//+use+comma+operator+to+ensure+expression+result+is+an+int
++++detail::writer+write;

++++using+expander+=+int[];
++++expander+{+0,+(write(std::forward<Ts>(Vals)),+0)...+};

++++//+write+the+final+linefeed
++++std::cout+<<+std::endl;
}

//+method+2+-+recursion

template<typename...Ts>
void+WriteLog2(Ts&&...ts)
{
++++detail::do_write(detail::writer(),+std::forward<Ts>(ts)...);
++++std::cout+<<+std::endl;
}

int+main()+{
++++WriteLog1("apple",+"orange",+"mango");
++++WriteLog1("apple",+"orange");
++++WriteLog1("apple");
++++WriteLog1("apple",+1.0,+"orange",+1L,+"mango",+2.6f);
++++WriteLog1();+//+test+pathalogical+case

++++WriteLog2("apple",+"orange",+"mango");
++++WriteLog2("apple",+"orange");
++++WriteLog2("apple");
++++WriteLog2("apple",+1.0,+"orange",+1L,+"mango",+2.6f);
++++WriteLog2();+//+test+pathalogical+case
++++return+0;
}|code-block|syntax|javascript|4958840|产出：|4958841|apple,+orange,+mango+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
apple,+orange++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
apple++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
apple,+1,+orange,+1,+mango,+2.6++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

apple,+orange,+mango+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
apple,+orange++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
apple++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
apple,+1,+orange,+1,+mango,+2.6

>++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++|4958842|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Q|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

I'll be honest with you, I've been writing c++11 template code for 4 years and I still have trouble remembering how to match the empty argument pack...

this little trick avoids recursive template expansion altogether:
(EDIT: re-written to support zero arguments and automatic comma separator insertion)

<pre><code>#include &lt;iostream&gt;

namespace detail {
 struct writer
 {
 template&lt;class T&gt;
 void operator()(const T&amp; t) {
 if (_first) {
 _first = false;
 }
 else {
 std::cout &lt;&lt; ", ";
 }
 std::cout &lt;&lt; t;
 }

 private:
 bool _first = true;
 };

 // non-template overload to catch no-parameter case
 void do_write(writer&amp;&amp;)
 {

 }

 // general case. Note w is passed by r-value reference
 // to allow the caller to construct it in-place 
 template&lt;typename T, typename...Ts&gt;
 void do_write(writer&amp;&amp; w, const T&amp; t, Ts&amp;&amp;...ts)
 {
 w(t);
 do_write(std::forward&lt;writer&gt;(w), std::forward&lt;Ts&gt;(ts)...);
 }


}

// method 1 - no recursion
template&lt;typename... Ts&gt;
void WriteLog1(Ts&amp;&amp;... Vals) {
 // expand one call for each parameter
 // use comma operator to ensure expression result is an int
 detail::writer write;

 using expander = int[];
 expander { 0, (write(std::forward&lt;Ts&gt;(Vals)), 0)... };

 // write the final linefeed
 std::cout &lt;&lt; std::endl;
}

// method 2 - recursion

template&lt;typename...Ts&gt;
void WriteLog2(Ts&amp;&amp;...ts)
{
 detail::do_write(detail::writer(), std::forward&lt;Ts&gt;(ts)...);
 std::cout &lt;&lt; std::endl;
}

int main() {
 WriteLog1("apple", "orange", "mango");
 WriteLog1("apple", "orange");
 WriteLog1("apple");
 WriteLog1("apple", 1.0, "orange", 1L, "mango", 2.6f);
 WriteLog1(); // test pathalogical case

 WriteLog2("apple", "orange", "mango");
 WriteLog2("apple", "orange");
 WriteLog2("apple");
 WriteLog2("apple", 1.0, "orange", 1L, "mango", 2.6f);
 WriteLog2(); // test pathalogical case
 return 0;
}
</code></pre>

output:

<pre><code>apple, orange, mango 
apple, orange 
apple 
apple, 1, orange, 1, mango, 2.6 

apple, orange, mango 
apple, orange 
apple 
apple, 1, orange, 1, mango, 2.6

&gt; 
</code></pre>

I am trying to understand how recursive variadic templates work.

<pre><code>#include &lt;iostream&gt;

template&lt;typename T&gt;
static inline void WriteLog(T&amp;&amp; msg) {
 std::wcout &lt;&lt; std::forward&lt;T&gt;(msg);
}

template&lt;typename T, typename... Ts&gt;
static void WriteLog(T&amp;&amp; msg, Ts&amp;&amp;... Vals) {
 WriteLog(std::forward&lt;T&gt;(msg));
 WriteLog(std::forward&lt;Ts&gt;(Vals)...);
 std::wcout &lt;&lt; "\n**End**";
}

int main() {
 WriteLog("apple, ", "orange, ", "mango");
}
</code></pre>

Output:

<pre><code>apple, orange, mango
**End**
**End**
</code></pre>

I expected only one <code>**End**</code>. Why is it printed twice?

c++11 recursive variadic templates

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我试图了解递归的各种模板是如何工作的。#include <iostream>template<typename T>static inline void WriteLog(T&& msg) { std::wcout << std::forward<T>(msg);}template<typename T, typename... Ts>static void WriteLog(T&& msg

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