blocks|key|876672|text|有几种方法可以做到这一点。所有这些都涉及到使用type_traits标头。例如，您可以在函数体中对相关类型进行静态断言。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|876673|或者，如果您需要在其他重载中考虑此功能，则可以使用SFINAE技术。|876674|template<typename+T>
auto+isFunction(const+T+&aVariable)+
++->+std::enable_if_t<std::is_same<T,+int>::value+%7C%7C+std::is_same<T,anEnum>::value,+bool>+{
}|code-block|syntax|javascript|876675|如果类型不匹配，这将在调用之前从重载集中删除该函数。但是，如果您不需要此行为，则静态断言确实允许更多程序员友好的错误消息。|876676|entityMap|0|LINK|mutability|MUTABLE|url|https://en.cppreference.com/w/cpp/header/type_traits^0|N|B|N|B|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@$9|Z|A|10|1|11]]|E|$]]|$1|F|3|G|5|6|7|12|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|13|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|14|8|@]|D|@]|E|$]]|$1|O|3|-4|5|6|7|15|8|@]|D|@]|E|$]]]|P|$Q|$5|R|S|T|E|$U|V]]]]

There are a couple of ways to accomplish this. All involve using the <a href="https://en.cppreference.com/w/cpp/header/type_traits" rel="noreferrer"><code>type_traits</code></a> header. You can static assert on the types in question in the body of the function, for instance.

Or, if you need to consider this function among other overloads, a SFINAE technique can be employed.

<pre><code>template&lt;typename T&gt;
auto isFunction(const T &amp;aVariable) 
 -&gt; std::enable_if_t&lt;std::is_same&lt;T, int&gt;::value || std::is_same&lt;T,anEnum&gt;::value, bool&gt; {
}
</code></pre>

This will remove the function from an overload set before it's called if the types don't match. But if you don't need this behavior, a static assertion does allow for a more programmer friendly error message.

blocks|key|876688|text|除了非C%2B%2B20的答案之外，如果您碰巧能够使用C%2B%2B20及其concepts特性，我建议您使用以下实现：|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|CODE|entityRanges|data|876689|#include+<iostream>
#include+<concepts>

enum+class+MyEnum+{
++++A,
++++B,
++++C
};

template+<typename+T>
concept+IntegralOrEnum+=+std::same_as<MyEnum,+T>+%7C%7C+std::integral<T>;

template+<IntegralOrEnum+T>
bool+isFunction(T+const&+aVariable)+{
++++return+true;
}

int+main()+{
++++isFunction(MyEnum::A);
++++isFunction(3);
++++isFunction("my_string");+//+error
++++return+0;
}|code-block|syntax|javascript|876690|Demo|876691|更新|876692|根据@RichardSmith的评论，这里有一个更具伸缩性和可重用性的方法：|876693|template+<typename+T,+typename+...U>
concept+one_of+=+(std::is_same_v<T,+U>+%7C%7C+...);

template+<one_of<int,+MyEnum>+T>
bool+isFunction(T+const&+aVariable)+{
++++return+true;
}|876694|entityMap|0|LINK|mutability|MUTABLE|url|https://en.cppreference.com/w/cpp/language/constraints|1|https://godbolt.org/#g:!((g:!((g:!((h:codeEditor,i:(fontScale:14,j:1,lang:c%2B%2B,selection:(endColumn:2,endLineNumber:23,positionColumn:1,positionLineNumber:1,selectionStartColumn:2,selectionStartLineNumber:23,startColumn:1,startLineNumber:1),source:'#include%2B%253Ciostream%253E#include%2B%253Cconcepts%253Eenum%2Bclass%2BMyEnum%2B{%2B%2B%2B%2BA,%2B%2B%2B%2BB,%2B%2B%2B%2BC};template%2B%253Ctypename%2BT%253Econcept%2BIntegralOrEnum%2B=%2Bstd::same_as%253CMyEnum,%2BT%253E%2B%7C%7C%2Bstd::integral%253CT%253E;template%2B%253CIntegralOrEnum%2BT%253Ebool%2BisFunction(T%2Bconst&%2BaVariable)%2B{%2B%2B%2B%2Breturn%2Btrue;}int%2Bmain()%2B{%2B%2B%2B%2BisFunction(MyEnum::A);%2B%2B%2B%2BisFunction(3);%2B%2B%2B%2BisFunction(|2|https://stackoverflow.com/users/1041090/richard-smith^0|N|5|U|8|U|8|0|0|0|0|4|1|0|0|2|0|2|D|2|0|0^^$0|@$1|2|3|4|5|6|7|15|8|@$9|16|A|17|B|C]|$9|18|A|19|B|D]]|E|@$9|1A|A|1B|1|1C]]|F|$]]|$1|G|3|H|5|I|7|1D|8|@]|E|@]|F|$J|K]]|$1|L|3|M|5|6|7|1E|8|@]|E|@$9|1F|A|1G|1|1H]]|F|$]]|$1|N|3|O|5|6|7|1I|8|@$9|1J|A|1K|B|C]]|E|@]|F|$]]|$1|P|3|Q|5|6|7|1L|8|@]|E|@$9|1M|A|1N|1|1O]]|F|$]]|$1|R|3|S|5|I|7|1P|8|@]|E|@]|F|$J|K]]|$1|T|3|-4|5|6|7|1Q|8|@]|E|@]|F|$]]]|U|$V|$5|W|X|Y|F|$Z|10]]|11|$5|W|X|Y|F|$Z|12]]|13|$5|W|X|Y|F|$Z|14]]]]

In addition to non-C++20 answer, if you are, by any chance, able to use C++20 and its <a href="https://en.cppreference.com/w/cpp/language/constraints" rel="nofollow noreferrer"><code>concepts</code></a> feature, I would suggest you the following implementation:

<pre class="lang-cpp prettyprint-override"><code>#include &lt;iostream&gt;
#include &lt;concepts&gt;

enum class MyEnum {
 A,
 B,
 C
};

template &lt;typename T&gt;
concept IntegralOrEnum = std::same_as&lt;MyEnum, T&gt; || std::integral&lt;T&gt;;

template &lt;IntegralOrEnum T&gt;
bool isFunction(T const&amp; aVariable) {
 return true;
}

int main() {
 isFunction(MyEnum::A);
 isFunction(3);
 isFunction("my_string"); // error
 return 0;
}
</code></pre>

<a href="https://godbolt.org/#g:!((g:!((g:!((h:codeEditor,i:(fontScale:14,j:1,lang:c%2B%2B,selection:(endColumn:2,endLineNumber:23,positionColumn:1,positionLineNumber:1,selectionStartColumn:2,selectionStartLineNumber:23,startColumn:1,startLineNumber:1),source:&#39;%23include+%3Ciostream%3E%0A%23include+%3Cconcepts%3E%0A%0Aenum+class+MyEnum+%7B%0A++++A,%0A++++B,%0A++++C%0A%7D%3B%0A%0Atemplate+%3Ctypename+T%3E%0Aconcept+IntegralOrEnum+%3D+std::same_as%3CMyEnum,+T%3E+%7C%7C+std::integral%3CT%3E%3B%0A%0Atemplate+%3CIntegralOrEnum+T%3E%0Abool+isFunction(T+const%26+aVariable)+%7B%0A++++return+true%3B%0A%7D%0A%0Aint+main()+%7B%0A++++isFunction(MyEnum::A)%3B%0A++++isFunction(3)%3B%0A++++isFunction(%22my_string%22)%3B+//+error%0A++++return+0%3B%0A%7D&#39;),l:&#39;5&#39;,n:&#39;0&#39;,o:&#39;C%2B%2B+source+%231&#39;,t:&#39;0&#39;)),k:49.85494633014216,l:&#39;4&#39;,n:&#39;0&#39;,o:&#39;&#39;,s:0,t:&#39;0&#39;),(g:!((g:!((h:compiler,i:(compiler:gsnapshot,filters:(b:&#39;0&#39;,binary:&#39;1&#39;,commentOnly:&#39;0&#39;,demangle:&#39;0&#39;,directives:&#39;0&#39;,execute:&#39;0&#39;,intel:&#39;0&#39;,libraryCode:&#39;1&#39;,trim:&#39;1&#39;),fontScale:14,j:2,lang:c%2B%2B,libs:!(),options:&#39;-std%3Dc%2B%2B2a&#39;,selection:(endColumn:1,endLineNumber:1,positionColumn:1,positionLineNumber:1,selectionStartColumn:1,selectionStartLineNumber:1,startColumn:1,startLineNumber:1),source:1),l:&#39;5&#39;,n:&#39;0&#39;,o:&#39;x86-64+gcc+(trunk)+(Editor+%231,+Compiler+%232)+C%2B%2B&#39;,t:&#39;0&#39;)),k:50.145053669857845,l:&#39;4&#39;,m:50,n:&#39;0&#39;,o:&#39;&#39;,s:0,t:&#39;0&#39;),(g:!((h:output,i:(compiler:2,editor:1,fontScale:14,wrap:&#39;1&#39;),l:&#39;5&#39;,n:&#39;0&#39;,o:&#39;%232+with+x86-64+gcc+(trunk)&#39;,t:&#39;0&#39;)),header:(),l:&#39;4&#39;,m:50,n:&#39;0&#39;,o:&#39;&#39;,s:0,t:&#39;0&#39;)),k:50.145053669857845,l:&#39;3&#39;,n:&#39;0&#39;,o:&#39;&#39;,t:&#39;0&#39;)),l:&#39;2&#39;,n:&#39;0&#39;,o:&#39;&#39;,t:&#39;0&#39;)),version:4" rel="nofollow noreferrer">Demo</a>

UPDATE

According to <a href="https://stackoverflow.com/users/1041090/richard-smith">@RichardSmith</a>'s comment, here is a more scalable and reusable approach:

<pre class="lang-cpp prettyprint-override"><code>template &lt;typename T, typename ...U&gt;
concept one_of = (std::is_same_v&lt;T, U&gt; || ...);

template &lt;one_of&lt;int, MyEnum&gt; T&gt;
bool isFunction(T const&amp; aVariable) {
 return true;
}
</code></pre>

blocks|key|563793|text|这个解决方案怎么样？如果类型T满足您的要求，则将编译带有该函数的代码。否则，静态断言将失败。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|563794|#include+<type_traits>
enum+anEnum+{
++++//
};

template+<typename+T,+bool+defined+=+std::is_same<T,+int>::value+%7C%7C
+++++++++++++++++++++++++++++++++++++std::is_same<T,+anEnum>::value>
bool+isFunction(const+T&+aVariable)
{
++++static_assert(defined,+"Invalid+specialization");

++++bool+result+=+false;
++++//+Put+your+code+here
++++return+result;
}|code-block|syntax|javascript|563795|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|$]]

What about this solution? A code with the function will be compiled if the type T is satisfied your requrements. Otherwise, the static assertion failed.

<pre><code>#include &lt;type_traits&gt;
enum anEnum {
 //
};

template &lt;typename T, bool defined = std::is_same&lt;T, int&gt;::value ||
 std::is_same&lt;T, anEnum&gt;::value&gt;
bool isFunction(const T&amp; aVariable)
{
 static_assert(defined, "Invalid specialization");

 bool result = false;
 // Put your code here
 return result;
}
</code></pre>

blocks|key|2880413|text|我改进了https://stackoverflow.com/a/60271100/12894563+answer。在这种情况下，‘in’可以提供帮助：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|2880414|template+<typename+T>
struct+always_false+:+std::false_type+{};

template+<typename+T>
bool+isFunction(const+T&+aVariable)
{
++++if+constexpr(std::is_same_v<T,+int>+%7C%7C+std::is_same_v<T,+anEnum>)
++++{
++++++++std::cout+<<+"int\n";
++++++++//+put+your+code+here
++++++++return+true;
++++}
++++else
++++{
++++++++static_assert(always_false<T>::value,+"You+should+declare+non-template+function+or+write+if+constexpr+branch+for+your+type");
++++++++return+false;
++++}
}

bool+isFunction(std::string_view)
{
++++std::cout+<<+"std::string_view\n";
++++return+true;
}

int+main()
{
++++isFunction(std::string_view("1L"));
++++isFunction(1);
++++//isFunction(1L);+//+will+produce+an+error+message+from+static_assert
}|code-block|syntax|javascript|2880415|isFunction(1L)将失败，因为没有重载函数或'if+constexpr‘分支。|2880416|更新:修复丢失的问题|2880417|template+<typename+T>
struct+always_false+:+std::false_type+{};|2880418|https://godbolt.org/z/eh4pVn|2880419|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/60271100/12894563|1^0|4|19|0|0|0|0|0|0|0|S|1|0^^$0|@$1|2|3|4|5|6|7|Z|8|@]|9|@$A|10|B|11|1|12]]|C|$]]|$1|D|3|E|5|F|7|13|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|14|8|@]|9|@]|C|$]]|$1|K|3|L|5|6|7|15|8|@]|9|@]|C|$]]|$1|M|3|N|5|F|7|16|8|@]|9|@]|C|$G|H]]|$1|O|3|P|5|6|7|17|8|@]|9|@$A|18|B|19|1|1A]]|C|$]]|$1|Q|3|-4|5|6|7|1B|8|@]|9|@]|C|$]]]|R|$S|$5|T|U|V|C|$W|X]]|Y|$5|T|U|V|C|$W|P]]]]

I've improved <a href="https://stackoverflow.com/a/60271100/12894563">https://stackoverflow.com/a/60271100/12894563</a> answer. 'If constexpr' can help in this situation:

<pre><code>template &lt;typename T&gt;
struct always_false : std::false_type {};

template &lt;typename T&gt;
bool isFunction(const T&amp; aVariable)
{
 if constexpr(std::is_same_v&lt;T, int&gt; || std::is_same_v&lt;T, anEnum&gt;)
 {
 std::cout &lt;&lt; "int\n";
 // put your code here
 return true;
 }
 else
 {
 static_assert(always_false&lt;T&gt;::value, "You should declare non-template function or write if constexpr branch for your type");
 return false;
 }
}

bool isFunction(std::string_view)
{
 std::cout &lt;&lt; "std::string_view\n";
 return true;
}

int main()
{
 isFunction(std::string_view("1L"));
 isFunction(1);
 //isFunction(1L); // will produce an error message from static_assert
}
</code></pre>

isFunction(1L) will fail becuase there is no overloaded function or 'if constexpr' branch.

UPDATE:
Fixed missed 

<pre><code>template &lt;typename T&gt;
struct always_false : std::false_type {};
</code></pre>

<a href="https://godbolt.org/z/eh4pVn" rel="nofollow noreferrer">https://godbolt.org/z/eh4pVn</a>

I am trying to define a function using templates and I want the typename to be either int or anEnum (a specific enum I had defined). I have tried the following but I have failed:

<pre><code>template &lt;int | anEnum T&gt; // or &lt;int T, anEnum T&gt; or &lt;int, anEnum T&gt;
bool isFunction(const T &amp;aVariable){}
</code></pre>

What I am trying to do is to use templates, instead of defining two overloaded functions.
I'd prefer the function to be called as the following, without the programmer having to consider the type

<pre><code>isFunction(aVariable) // and not isFunction&lt;int&gt; (aVariable) nor isFunction&lt;anEnum&gt; (aVariable)
</code></pre>

Basically, I want this function to be templated for int and aNum types. I have searched for this, but could not find the answer. What may I be missing? Thank you,

Overloading a function using 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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我正在尝试使用模板定义一个函数，并且我希望typename为int或anEnum (我定义的一个特定枚举)。我尝试过以下几种方法，但都失败了：template <int | anEnum T> // or <int T, anEnum T> or <int, anEnum T>bool isFunction(const...

问使用模板重载函数
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