问题描述
假设我有一个名为 c > / std :: vector< QVector< ...>> 重载。
I may also need to add float overloads, or QVector<std::vector<...>> / std::vector<QVector<...>> overloads.
基本上，这是一个我想归纳出大量的重载。
Basically, it's a huge set of overloads that I'd like to generalize.
是否可以将所有重载组合成2个函数模板（一个用于1D容器，另一个用于2D容器）？
Is it possible to combine all of them into maybe 2 function templates (one for 1D containers, another for 2D containers)?
谢谢
推荐答案
是...需要一些工作，但是相对简单。
Yes... require a little work but is relatively simple.
也许有更简单的方法，但是我建议创建一个自定义类型特征，以验证模板模板是否为 std :: vector 或 QVector
Maybe there are simpler methods but I propose the create a custom type traits that verify if a template-template is std::vector or QVector
template <template <typename...> class>
struct isVector : public std::false_type
{ };
template <>
struct isVector<std::vector> : public std::true_type
{ };
template <>
struct isVector<QVector> : public std::true_type
{ };
下一个自定义类型特征可以验证类型是否为<$ c $的浮点类型c> std :: complex< T> 类型
Next another custom type traits to verify if a type is a floating point type of a std::complex<T> type
template <typename T>
struct isCFloating : public std::is_floating_point<T>
{ };
template <typename T>
struct isCFloating<std::complex<T>> : public std::true_type
{ };
现在您可以编写向量版本（截取也混合了 std :: vector / QVector 情况），如下所示
Now you can write the vector-of-vector version (that intercept also mixed std::vector/QVector case) as follows
template <template <typename ...> class V1,
template <typename ...> class V2, typename T>
auto loadData (V1<V2<T>> & v, std::string fn)
-> std::enable_if_t< isVector<V1>::value
&& isVector<V2>::value
&& isCFloating<T>::value>
{
std::cout << "- vector of vector version, " << fn << std::endl;
}
，然后是简单的矢量版本（包装第一个参数并调用向量版本）变成
and, after, the simple vector version (that wrap the first argument and call the vector-of-vector version) become
template <template <typename ...> class V, typename T>
auto loadData (V<T> & v, std::string fn)
-> std::enable_if_t<isVector<V>::value && isCFloating<T>::value>
{
std::cout << "- vector version, " << fn << std::endl;
V<V<T>> vv{1, v};
loadData(vv, fn);
}
我准备了以下完整的示例，但（抱歉）我没有目前没有可用的QT平台，所以我添加了一个假的 QVector
I've prepared the following full working example but (sorry) I don't have a QT platform available at the moment so I have added a fake QVector
#include <vector>
#include <complex>
#include <iostream>
#include <type_traits>
// fake QVector
template <typename>
struct QVector
{
template <typename ... Ts>
QVector (Ts const & ...)
{ }
};
template <template <typename...> class>
struct isVector : public std::false_type
{ };
template <>
struct isVector<std::vector> : public std::true_type
{ };
template <>
struct isVector<QVector> : public std::true_type
{ };
template <typename T>
struct isCFloating : public std::is_floating_point<T>
{ };
template <typename T>
struct isCFloating<std::complex<T>> : public std::true_type
{ };
template <template <typename ...> class V1,
template <typename ...> class V2, typename T>
auto loadData (V1<V2<T>> & v, std::string fn)
-> std::enable_if_t< isVector<V1>::value
&& isVector<V2>::value
&& isCFloating<T>::value>
{
std::cout << "- vector of vector version, " << fn << std::endl;
}
template <template <typename ...> class V, typename T>
auto loadData (V<T> & v, std::string fn)
-> std::enable_if_t<isVector<V>::value && isCFloating<T>::value>
{
std::cout << "- vector version, " << fn << std::endl;
V<V<T>> vv{1, v};
loadData(vv, fn);
}
int main ()
{
std::vector<float> vf;
std::vector<std::complex<float>> vc;
std::vector<std::vector<double>> vvf;
std::vector<std::vector<std::complex<double>>> vvc;
QVector<long double> qf;
QVector<std::complex<long double>> qc;
QVector<QVector<float>> qqf;
QVector<QVector<std::complex<float>>> qqc;
loadData(vf, "case 1");
loadData(qf, "case 2");
loadData(vc, "case 3");
loadData(qc, "case 4");
loadData(vvf, "case 5");
loadData(qqf, "case 6");
loadData(vvc, "case 7");
loadData(qqc, "case 8");
// extra cases: mixing std::vector and QVector
std::vector<QVector<double>> vqf;
std::vector<QVector<std::complex<double>>> vqc;
QVector<std::vector<long double>> qvf;
QVector<std::vector<std::complex<long double>>> qvc;
loadData(vqf, "case 9");
loadData(vqc, "case 10");
loadData(qvf, "case 11");
loadData(qvc, "case 12");
}
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