blocks|key|758437|text|请注意，您可能有以下内容：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|758438|template+<class+T,
++++++++++template+<class>+class+Policy1,
++++++++++template+<class>+class+Policy2,
++++++++++template+<class>+class+Policy3>
struct+PolicyClass+:+public+Policy1<ObjT>,
+++++++++++++++++++++public+Policy2<ObjT>,
+++++++++++++++++++++public+Policy3<ObjT>
{};

template+<class+T>+struct+implementedPolicy1+{};
template+<class+T>+struct+implementedPolicy2+{};
template+<class+T,+class+A>+struct+implementedPolicy3+{};

//+Adapt+the+policy+interface
template+<class+T>
using+myImplementedPolicy3+=+implementedPolicy3<T,+AType>;+//+Assuming+AType+exist

PolicyClass+<ObjT,+implementedPolicy1,+implementedPolicy2,+myImplementedPolicy3>+policies;|code-block|syntax|javascript|758439|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|$]]

Note that you may have something like:

<pre><code>template &lt;class T,
 template &lt;class&gt; class Policy1,
 template &lt;class&gt; class Policy2,
 template &lt;class&gt; class Policy3&gt;
struct PolicyClass : public Policy1&lt;ObjT&gt;,
 public Policy2&lt;ObjT&gt;,
 public Policy3&lt;ObjT&gt;
{};

template &lt;class T&gt; struct implementedPolicy1 {};
template &lt;class T&gt; struct implementedPolicy2 {};
template &lt;class T, class A&gt; struct implementedPolicy3 {};

// Adapt the policy interface
template &lt;class T&gt;
using myImplementedPolicy3 = implementedPolicy3&lt;T, AType&gt;; // Assuming AType exist

PolicyClass &lt;ObjT, implementedPolicy1, implementedPolicy2, myImplementedPolicy3&gt; policies;
</code></pre>

blocks|key|758457|text|您需要能够在包之间进行分隔。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|758458|//+helper+template.++Using+`std::tuple<>`+instead+is+another+option.
template<class...>struct+type_list+{};

//+base,+note+no+body:
template+<
++++class+T,
++++template+<class,+typename...>+++class+Policy0,
++++template+<class,+typename...>+++class+Policy1,
++++template+<class,+typename...>+++class+Policy2,
++++typename...+Packs
>
struct+PolicyClass;

//+specialization:
template+<
++++class+T,
++++template+<class,+typename...>+++class+Policy0,
++++template+<class,+typename...>+++class+Policy1,
++++template+<class,+typename...>+++class+Policy2,
++++typename...+A0s,
++++typename...+A1s,
++++typename...+A2s
>
struct+PolicyClass<
++T,+Policy1,+Policy2,+Policy3,
++type_list<A0s...>,+type_list<A1s...>,+type_list<A2s...>
>
:+Policy0<T,+A0s...>,+Policy1<T,+A1s...>,+Policy2<T,+A2s...>+{}|code-block|syntax|javascript|758459|在这里，我将每个策略额外的参数打包到一个type_list中。|offset|length|style|CODE|758460|从理论上讲，你可以做一些更花哨的事情，比如让特定的“标签”类型作为分隔符，但它最终会成为很多体操项目。|758461|PolicyClass<+int,+bob,+eve,+alice,+type_list<>,+type_list<double>,+type_list<char,+char,+char>+>+foo;|758462|会创造|758463|PolicyClass:+bob<int>,+alice<int,+double>,+eve<int,+char,+char,+char>|758464|粗略地说。|758465|entityMap^0|0|0|K|9|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|Z|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|10|8|@$I|11|J|12|K|L]]|9|@]|A|$]]|$1|M|3|N|5|6|7|13|8|@]|9|@]|A|$]]|$1|O|3|P|5|D|7|14|8|@]|9|@]|A|$E|F]]|$1|Q|3|R|5|6|7|15|8|@]|9|@]|A|$]]|$1|S|3|T|5|D|7|16|8|@]|9|@]|A|$E|F]]|$1|U|3|V|5|6|7|17|8|@]|9|@]|A|$]]|$1|W|3|-4|5|6|7|18|8|@]|9|@]|A|$]]]|X|$]]

You need to be able to delimit between the packs.

<pre><code>// helper template. Using `std::tuple&lt;&gt;` instead is another option.
template&lt;class...&gt;struct type_list {};

// base, note no body:
template &lt;
 class T,
 template &lt;class, typename...&gt; class Policy0,
 template &lt;class, typename...&gt; class Policy1,
 template &lt;class, typename...&gt; class Policy2,
 typename... Packs
&gt;
struct PolicyClass;

// specialization:
template &lt;
 class T,
 template &lt;class, typename...&gt; class Policy0,
 template &lt;class, typename...&gt; class Policy1,
 template &lt;class, typename...&gt; class Policy2,
 typename... A0s,
 typename... A1s,
 typename... A2s
&gt;
struct PolicyClass&lt;
 T, Policy1, Policy2, Policy3,
 type_list&lt;A0s...&gt;, type_list&lt;A1s...&gt;, type_list&lt;A2s...&gt;
&gt;
: Policy0&lt;T, A0s...&gt;, Policy1&lt;T, A1s...&gt;, Policy2&lt;T, A2s...&gt; {}
</code></pre>

where I pack each policies extra arguments into a <code>type_list</code>.

In theory you could do fancier things, like have particular "tag" types being the delimiters, but it ends up being a lot of gymnastics.

<pre><code>PolicyClass&lt; int, bob, eve, alice, type_list&lt;&gt;, type_list&lt;double&gt;, type_list&lt;char, char, char&gt; &gt; foo;
</code></pre>

will create

<pre><code>PolicyClass: bob&lt;int&gt;, alice&lt;int, double&gt;, eve&lt;int, char, char, char&gt;
</code></pre>

roughly.

blocks|key|1301753|text|我从来没有喜欢过模板参数，这是我要避免的另一个例子：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1301754|template+<typename+T,+typename...+Policies>
struct+PolicyClass:+Policies...+{};|code-block|syntax|javascript|1301755|将只适用于任意的策略：|1301756|using+PC+=+PolicyClass<int,
+++++++++++++++++++++++LifetimePolicy<LP::Extended>,
+++++++++++++++++++++++DurabilityPolicy<3600,+DP::Seconds>
+++++++++++++++++++++++StoragePolicy<int,+SP::InMemory>>;|1301757|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

I have never been fan of template template parameters, and this is one other instance I would avoid them:

<pre><code>template &lt;typename T, typename... Policies&gt;
struct PolicyClass: Policies... {};
</code></pre>

will just work with arbitrary policies:

<pre><code>using PC = PolicyClass&lt;int,
 LifetimePolicy&lt;LP::Extended&gt;,
 DurabilityPolicy&lt;3600, DP::Seconds&gt;
 StoragePolicy&lt;int, SP::InMemory&gt;&gt;;
</code></pre>

I am wondering if it's possible to combine policy classes using variadic template-template parameters such that each policy may have it's own template pack. It seems like you can only share a single template pack amongst all policies but I hope that's not the case.

The following seems to be what's possible:

<pre><code>template &lt;
 class T,
 template &lt;class, typename...&gt; class Policy1,
 template &lt;class, typename...&gt; class Policy2,
 template &lt;class, typename...&gt; class Policy3,
 typename... Args 
&gt;
struct PolicyClass 
 : public Policy1 &lt;ObjT, Args...&gt;
 , public Policy2 &lt;ObjT, Args...&gt;
 , public Policy3 &lt;ObjT, Args...&gt; {}
</code></pre>

I'm hoping each policy can have it's own pack so I could make something like this (?):

<pre><code>template &lt;class T&gt;
struct implementedPolicy1 {};
template &lt;class T&gt;
struct implementedPolicy2 {};
template &lt;class T, class A&gt;
struct implementedPolicy3 {};

PolicyClass &lt;ObjT, 
 implementedPolicy1,
 implementedPolicy2,
 implementedPolicy3&lt;AType&gt;
 &gt;
</code></pre>

The idea being each of the policies are all using the same object type but the third has some further templating. I know that's incorrect code above - just trying to illustrate what I'd like to be able to do.

Thanks

Combining Policy Classes - Template Template Parameters & 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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我想知道是否可以使用各种模板-模板参数组合策略类，以便每个策略都有自己的模板包。似乎您只能在所有策略中共享一个模板包，但我希望不是这样。以下几点似乎是可能的：template < class T, template <class, typename...> class Policy1, templ...

问组合策略类-模板参数和可变模板
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