initialize an array using const values using a template compilation-time computation

Question

I'm trying to write something like this :

template <typename type,int p,int q = 1> struct const4array
    {
    static const type value [] = { type(p)/type(q) , type(p)/type(q) , type(p)/type(q) , type(1) } ;
    };

double xx [] = { 0.5 , 0.5 , 0.5 , 1 } ;
double yy [] = const4array<double,1,2>::value ; // I would like to have : xx == yy

I think this code is easy to understand for a human developer, but apparently not for the compiler (it returns many errors).

Is it possible to do what I want, and if it is, how to do it properly? (I found many other questions that looks like this one, but not close enough to match mine).

Thanks in advance!

I think, it is broken by the same reason why double zz[] = xx; doesn't work as well. I tried on godbolt — Scheff's Cat
– Scheff's Cat, Commented Jul 7, 2019 at 12:43

Some programmer dude · Accepted Answer · 2019-07-07 12:44:37Z

1

Plain C-style arrays can only be initialized using {} syntax, they can't be copy-initialized from other arrays. You can however use objects emulating or wrapping arrays (like std::array) as those can be copied and used for initialization.

answered Jul 7, 2019 at 12:44

Some programmer dude

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