如何限制我的模板仅接受具有特定输入和参数的 lambda输出类型？
受到计算函数泰勒级数的其他问题的启发（原始问题），我编写了一个模板没有任何限制来成功计算总和。这是当前代码（模板主体已删除，正如 @Elliott 所说，这与要点无关..）
#include <iostream>
#include <cmath>
#include <limits>
template<typename ftn>
long double Taylor_sum(ftn terms_to_sum) { /* Summation calculation goes here... */ return result; };
int main(){
using namespace std; long double x; cin >> x ;
long double series_sum = Taylor_sum([x](unsigned long long int i) -> long double { return /*Taylor term here*/; });
if (!isfinite(series_sum)) cout << "Series does not converge!" << endl;
else {
cout << "Series converged, its value is : " << series_sum << endl;
cout << "Compared to sin : " << sinl(x) << endl;
}
}
：自己实践概念，我试图限制模板仅接受以unsigned long long int作为输入的lambda，以及long double作为输出。这是我当前的尝试（无法编译）：
template<typename T,integral ARG>
concept my_lambda = requires(T t, ARG u) {
{ return t(u); };
}
template<my_lambda ftn>
long double Taylor_sum(ftn term) { //The rest is same...
我用 google 搜索了各种来源，但在我看来，由于 concept 是 C++20 中相对较新的功能，因此可用的材料似乎较少。有谁知道如何正确限制我的模板参数？
Inspired by other question to calculate taylor series of a function(Original question), I wrote a template without any constraint to successfully calculate the sum. Here is current code (Template body removed, as @Elliott says it's irrelevant to the point..):
#include <iostream>
#include <cmath>
#include <limits>
template<typename ftn>
long double Taylor_sum(ftn terms_to_sum) { /* Summation calculation goes here... */ return result; };
int main(){
using namespace std; long double x; cin >> x ;
long double series_sum = Taylor_sum([x](unsigned long long int i) -> long double { return /*Taylor term here*/; });
if (!isfinite(series_sum)) cout << "Series does not converge!" << endl;
else {
cout << "Series converged, its value is : " << series_sum << endl;
cout << "Compared to sin : " << sinl(x) << endl;
}
}
Although the code works enough, to study & practice the concept myself, I am trying to constrain the template to accept only lambda with unsigned long long int as a input, and long double as output. Here is my current attempt (which does not compile):
template<typename T,integral ARG>
concept my_lambda = requires(T t, ARG u) {
{ return t(u); };
}
template<my_lambda ftn>
long double Taylor_sum(ftn term) { //The rest is same...
I googled various sources, but it seems to me that because the concept is relatively new feature in C++20, there seems less material available. Does anyone know how to constrain my template parameter properly?
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评论（2）
您可以将复合要求与return-type-requirement:
演示
You can use compound requirements with return-type-requirement:
Demo
对我来说，解决方案是 std::convertible_to 和 std::function 看起来相当简洁：
To me, a solution with std::convertible_to and std::function looks quite concise: