Implicit Conversion for fine::Ok and fine::Error #13
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This rework ensures that `fine::Ok` and `fine::Error` can correctly convert when used in conjunction with container types like `std::variant`. The downside to this approach, as implemented, is the need to go through 2 factory functions, `fine::ok` and `fine::error`, to construct these.
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Class Template Argument Deduction allows class templates to be inferred from constructor arguments, which removes the need for `fine::ok` and `fine::error` as special factory functions.
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| std::variant<fine::Ok<int64_t>, fine::Error<std::string>> find_meaning(ErlNifEnv *env) { | ||
| if (...) { | ||
| return fine::Error<std::string>("something went wrong"); | ||
| std::variant<fine::Ok<int64_t, int64_t>, fine::Error<std::string>> divmod(ErlNifEnv *env, int64_t a, int64_t b) { |
c_include/fine.hpp
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| template <typename = std::enable_if_t<std::is_default_constructible_v<Items>>> | ||
| Ok() : m_items() {} |
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We know that std::tuple<>() is constructible, so we don't need this conditional?
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| template <typename = std::enable_if_t<std::is_default_constructible_v<Items>>> | |
| Ok() : m_items() {} | |
| Ok() : m_items() {} |
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A remnant from trying to understand and make the template code works. I though I still needed it.
It is analogous to Ok<Args...>::Ok(Args...) with an empty parameter pack.
Also, keeping this would enable constructing like so:
return fine::Ok<std::string> {};Which I don't think is wanted.
jonatanklosko
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Aug 14, 2025
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This rework ensures that
fine::Okandfine::Errorcan correctly convert when used in conjunction with container types likestd::variant.This is an alternative to #12. Instead of exposing a result type, we ensure that conversions when
fine::Okandfine::Errorwithstd::variantwork as expected.The downside to this implementation is the need to go through 2 factory functions,fine::okandfine::error, to construct these correctly. I believe this problem could be solved, like CTAD is applicable to tuples, but it would require a lot more template metaprogramming to get everything working correctly.