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Re: Indexes in ranged loops for all containers

From: Kilian Henneberger <kilis-mail_at_[hidden]>
Date: Wed, 4 May 2022 22:39:33 +0200
Am 04.05.2022 um 21:56 schrieb Jens Maurer via Std-Discussion:
> On 04/05/2022 21.43, Joey Pendergrast via Std-Discussion wrote:
>> I like the way that std::map gives the key and value for ranged loops:
>> for (auto& [key, value] : my_map)
>> Why don't other containers allow for the "index" to also be gotten in a similar way?
>> for (auto& [index, value] : any_container) would be convenient to have as well.
>> Or, can this be done, but I'm just unaware? Thanks in advance.
> Maybe something like
> for (auto& [value, index] : std::views::zip_view(my_vector, std::views::iota_view(0, my_vector.size()))) { ...}
> could work.
> Jens

The correct syntax in C++23 will be:

for (auto [value, index] : std::views::zip(my_vector,
std::views::iota(0)) { ... }

You have to use "auto [value, index]" or "auto&& [value, index]" as
dereferencing a zip_view::iterator returns a std::pair (or std::tuple)
by value.
Additionally, P2164R5 <https://wg21.link/p2164r5> proposes
std::views::enumerate for C++26.
In P2214R0
is explained, why enumerate differs from zip + iota.

Best regards,

Received on 2022-05-04 20:39:36