How to fill a vector with typeid's from variadic template arguments

Question

std::vector<std::type_index> vec;

template <typename T1, typename... Tn>
void Fill() {
    vec.push_back(typeid(T1));
    // fill the vector with the remaining type ids
}

I want to fill the vector with the typeids of the template arguments. How could I implement this?

This question may be related to your problem: [**Creating an array initializer from a tuple or variadic template parameters**](http://stackoverflow.com/questions/18251815/creating-an-array-initializer-from-a-tuple-or-variadic-template-parameters). Note that the templated parameters are evaluated at compile time. — πάντα ῥεῖ, May 02 '14 at 13:52

score 10 · Accepted Answer · answered May 02 '14 at 14:32

10

The following solution uses intializer list:

template <typename... Types>
void Fill(std::vector<std::type_index>& vec)
{
    vec.insert(vec.end(), {typeid(Types)...});
}

See live example.

answered May 02 '14 at 14:32

Constructor

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This seems to be the shortest and most effective solution. – Appleshell May 02 '14 at 14:47

score 4 · Answer 2 · answered May 02 '14 at 13:56

4

This should work:

template<typename T>
void Fill() {
    vec.push_back(typeid(T));
}

template <typename T1, typename T2, typename... Tn>
void Fill() {
    Fill<T1>();
    Fill<T2, Tn...>();
}

Live example

answered May 02 '14 at 13:56

Daniel Frey

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RamblingMad · Answer 3 · 2014-05-02T14:00:26.793

2

Implement it using recursion:

std::vector<std::type_index> vec;

template<typename T>
void fill(){
    vec.emplace_back(typeid(T)); // pretty sure you want emplace_back here ;)
}

template<typename T1, typename T2, typename ... Tn>
void fill(){
    fill<T1>();
    fill<T2, Tn...>();
}

I think this will do what you want.

edited May 02 '14 at 14:00

answered May 02 '14 at 13:49

RamblingMad

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I really don't understand why you had to downvote though, just a comment would have been far more constructive :/ – RamblingMad May 02 '14 at 14:02
If you are referring to me: I didn't downvote. In fact I just got a downvote myself which I don't understand. (I just checked: You don't have a downvote. You have 1 upvote and 0 downvotes!) – Daniel Frey May 02 '14 at 14:03
Oh, my bad then, still don't get the down-vote though – RamblingMad May 02 '14 at 14:03
@CoffeeandCode Which downvote? I just retracted my former upvote, in favor of the other answer. – πάντα ῥεῖ May 02 '14 at 14:08
@DanielFrey no. filler sentence. – RamblingMad May 02 '14 at 14:18
@CoffeeandCode OK, so in case of doubt I'll believe you that you downvoted someone else today. – Daniel Frey May 02 '14 at 14:19
Why would I lie about that -_- I down-voted the question, but not your answer. – RamblingMad May 02 '14 at 14:22
@CoffeeandCode And what was this meant to be?? (flagged as not constructive ...) – πάντα ῥεῖ May 02 '14 at 14:22
@πάνταῥεῖ What do you mean? This was the first answer to the question. I did edit it later to correct it though, as Daniel pointed out to me – RamblingMad May 02 '14 at 14:24
1

@CoffeeandCode Downvoting the question is free and therefore doesn't explain why your reputation was 409 yesterday and it's 428 now. You downvoted an answer today, that's why I was suspicious if it was my answer... sorry if I jumped to the wrong conclusion. – Daniel Frey May 02 '14 at 14:24
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@πάνταῥεῖ it was satire. Geez, sometimes the community is pretty stiff here :L – RamblingMad May 02 '14 at 14:27
@CoffeeandCode Hmmm, satire or not may lie in the eye of the viewer. Be a bit cautios with such. I'm not that _stiff_ as you might think I am ;) ... – πάντα ῥεῖ May 02 '14 at 14:30

How to fill a vector with typeid's from variadic template arguments

3 Answers3