Here is the list of all current C++ metaprogramming kata. Most of them deal with general TMP and not restricted to tuples (although you can use tuples as a means to solve them). The only tuple-heavy one is this beta. It dives into tuples more than this task.

... that are numbers

This is not enough imo. The description should be more explicit about what it allows (or disallows). For example, char is explicitly excluded, but most solutions (including mine) also count any non-char integral type like bool and char32_t, which aren't tested. Moreover, if an answer only hardcodes double and int, are they not excluding other valid numeral types like std::size_t or long? I'm not saying these types should be tested at all - but the description should upfront be clear that it is only testing int and double. It signals that the solver should not strive for total correctness, and should instead make assumptions. Sounds like overthinking, but solvers can't see the submission tests and so can't tell what assumptions are being implicitly made.

Regular sizeof should be exempt from the restrictions. You can use it as a part of a valid answer. Only sizeof... should be disabled.

Can someone please explain me this piece of code? what is id?

That's true, but there is no better way to do it, short of resorting to a higher-precision floating-point type.

You forgot for double inprecision, basicly floating-point arithmetic, not a good idea.

in test example 3.14 and 42 are equal to 45.14, this is clear, but i wonder where did 0.001 come from?

Awesome Kata! C++ tuples are insane to work with! Can you suggest me more Katas similar to yours?

https://www.codewars.com/kata/reviews/5883785e512b0330ff0003c9/groups/64f00dae18408b0001497ac8

https://www.codewars.com/kata/reviews/58847cf4a3dd74693e000114/groups/64f00d7318408b0001497abf

Clever (4,7s) but not best practice.... Sorry....(my code = 3,9s, but not clever :-( )

Solution of O(nlogn) complexity for O(n) problem, though

it is pass-by-value since the & was removed. So the input parameters are in fact copies. The code is fuly eqivalent to the function taking const& and then making explicit copies.