Template deduction guide fails with 'too many initializers' error

Question

I was reading on template deduction then tried to create one. as follows:-

#include <iostream>
#include <array>
using namespace std;
template<int i,typename A,typename... B> struct deducted{

};
//Deduction guide
template<typename A,typename... B> deducted(A a,B... b)->deducted<0,A,B...>;
//

int main(){
    deducted a={"","",""};
    deducted b={0,0,0};
    array c={0,0,0};
}

what supprises me is the test fails with error: too many initializers for 'deducted<0, const char*, const char*, const char*>' but the std::array version works fine. What could i be possibly missing, and can anyone rewrite much better?

Jarod42 · Answer 1 · 2020-11-21T11:14:06.980

1

Deduction works, but then, construction fails.

Provide constructor. (or appropriate members for aggregate initialization).

edited Nov 21 '20 at 11:14

answered Nov 21 '20 at 11:06

Jarod42

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I don't see a constructor [here](https://en.cppreference.com/w/cpp/header/array). So i tried copy the same. – D. Sikilai Nov 21 '20 at 11:09
There is the aggregate initialization. – Jarod42 Nov 21 '20 at 11:13

Ted Lyngmo · Accepted Answer · 2020-11-21T11:17:34.807

1

You have too many initializers because there's noting to receive what you initialize it with.

Example fix:

#include <type_traits>

template<int i, typename A, typename... B>
struct deducted{
    A a;
    std::common_type_t<B...> arr[sizeof...(B)];
};

Demo

edited Nov 21 '20 at 11:17

answered Nov 21 '20 at 11:12

Ted Lyngmo

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Template deduction guide fails with 'too many initializers' error

2 Answers2