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P2996 - example of enum_to_string via switch-case #164

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27 changes: 27 additions & 0 deletions 2996_reflection/reflection.md
Original file line number Diff line number Diff line change
Expand Up @@ -499,6 +499,33 @@ Note that this last version has lower complexity: While the versions using an ex

On Compiler Explorer: [EDG](https://godbolt.org/z/Y5va8MqzG), [Clang](https://godbolt.org/z/Kfqc77rMq).

We can even generate switch-case. For instance we can use `deducing this` with a nested switch-case.

::: bq
```c++
template <typename E> requires std::is_enum_v<E>
constexpr auto enum_to_string(E value) {
static constexpr auto enumerators = std::meta::enumerators_of(^E);
return [value]<std::size_t I = 0u>(this auto&& self) -> std::optional<std::string_view> {
switch (value) {
default:
if constexpr (I < std::size(enumerators) - 1)
return self.template operator()<I + 1>();
else
return std::nullopt;
case [: enumerators[I] :]:
return std::meta::name_of(enumerators[I]);
}
}();
}
```
:::

Note that this version optimizations depends on the compiler ability to flatten nested switch-case and it will be able to rewritten with the code generation abilities in the future versions.

On Compiler Explorer: [Clang](https://godbolt.org/z/Mc5Yvsrxc)

:::

Many many variations of these functions are possible and beneficial depending on the needs of the client code.
For example:
Expand Down