Should we "propagate const-ness" when doing structured binding?

[lanyizi]

Currently this surprisingly compiles:
https://godbolt.org/z/Ees7KfxzP

I don't have much knowledge on structured binding, but I guess it's related to the return type of this function?

json/include/nlohmann/detail/iterators/iteration_proxy.hpp

Line 156 in 4f8fba1

auto get(const nlohmann::detail::iteration_proxy_value<IteratorType>& i) -> decltype(i.value())

[gregmarr]

The const here refers to the temporary that is implicitly constructed by the structured bindings.

for (auto const& [key, value] : json.items()) {
    value.at(1) = 5;
}

This is basically equivalent to this, which also compiles:

for (auto const& item : json.items()) {
    auto &key = item.key();
    auto &value = item.value();
    value.at(1) = 5;
}