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libutil: Replace hand-rolled enumerate with std::views::{zip,iota}

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It would have been nice to use std::views::enumerate here, but
it uses a signed difference type for the value_type:

> value_type = std::tuple<difference_type, ranges::range_value_t<Base>>

zip + iota has the same semantics as the code used to have, so there's
no behavior change here.
This commit is contained in:
Sergei Zimmerman 2025-08-22 03:04:59 +03:00
parent d7612f350f
commit b853994e7a
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1 changed files with 6 additions and 47 deletions
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53
src/libutil/include/nix/util/util.hh
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@ -4,13 +4,13 @@
#include "nix/util/types.hh" #include "nix/util/types.hh"
#include "nix/util/error.hh" #include "nix/util/error.hh"
#include "nix/util/logging.hh" #include "nix/util/logging.hh"
#include "nix/util/strings.hh"
#include <functional> #include <functional>
#include <map> #include <map>
#include <sstream> #include <sstream>
#include <optional> #include <optional>
#include <ranges>
#include "nix/util/strings.hh"
namespace nix { namespace nix {
@ -300,53 +300,12 @@ struct MaintainCount
/** /**
* A Rust/Python-like enumerate() iterator adapter. * A Rust/Python-like enumerate() iterator adapter.
*
* Borrowed from http://reedbeta.com/blog/python-like-enumerate-in-cpp17.
*/ */
template< template<std::ranges::viewable_range R>
typename T, constexpr auto enumerate(R && range)
typename TIter = decltype(std::begin(std::declval<T>())),
typename = decltype(std::end(std::declval<T>()))>
constexpr auto enumerate(T && iterable)
{ {
struct iterator /* Not std::views::enumerate because it uses difference_type for the index. */
{ return std::views::zip(std::views::iota(size_t{0}), std::forward<R>(range));
size_t i;
TIter iter;
constexpr bool operator!=(const iterator & other) const
{
return iter != other.iter;
}
constexpr void operator++()
{
++i;
++iter;
}
constexpr auto operator*() const
{
return std::tie(i, *iter);
}
};
struct iterable_wrapper
{
T iterable;
constexpr auto begin()
{
return iterator{0, std::begin(iterable)};
}
constexpr auto end()
{
return iterator{0, std::end(iterable)};
}
};
return iterable_wrapper{std::forward<T>(iterable)};
} }
/** /**