Reflection tutorial - #146
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RyanJK5
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Really happy with how this came out. It keeps the relevant parts of reflection in clear focus.
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| // We use `throw` inside a `consteval` block rather than `static_assert` | ||
| // or `EXPECT_*`: `static_assert` needs `members` to independently be a | ||
| // constant expression, and `EXPECT_*`'s comparison helpers aren't | ||
| // `constexpr` functions. |
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This code probably do with a one-sentence explanation of what a consteval block is.
| // `e` is a loop variable, not a constant expression, so we can't | ||
| // splice it with `return [:e:];`. `extract<Suit>(e)` only needs a | ||
| // value, not a fixed compile-time constant. | ||
| return extract<Suit>(e); |
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I really like how naturally this was introduced.
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| TEST(TutorialsReflection, Substitute) { | ||
| // `substitute(^^Template, {args...})` instantiates a template from infos; | ||
| // `reflect_constant` turns an ordinary value into an info usable as a | ||
| // non-type template argument. | ||
| // clang-format off | ||
| constexpr std::meta::info array_info = | ||
| substitute(^^std::array, {^^double, std::meta::reflect_constant(3)}); | ||
| // clang-format on | ||
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| static_assert(std::is_same_v<typename[:array_info:], std::array<double, 3>>); | ||
| } |
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I think this could benefit from a comment explaining the use case of substitute - when you want to use a reflection in a consteval context even though it itself is not a constant expression.
For me, at least, I found the distinction between constant expressions and consteval to be one of the more difficult topics when first learning reflection.
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| constexpr std::ranges::range auto member_functions = std::define_static_array( | ||
| members_of(^^Point, std::meta::access_context::current()) | | ||
| std::views::filter([](std::meta::info member) { | ||
| return is_function(member) && has_identifier(member); | ||
| })); | ||
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nit: I would prefer to write this as two separate filters, but I'm more than happy to approve whatever you or others find more readable. (below code is not clang-formatted)
constexpr std::ranges::range auto member_functions = std::define_static_array(
members_of(^^Point, std::meta::access_context::current())
| std::views::filter(std::meta::is_function)
| std::views::filter(std::meta::has_identifier));
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