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Improve Middleware documentation and compile time static assertions #864

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6359caf
added contains_decayed to black_magic
Guiorgy Aug 6, 2024
9bf2f1e
added is_superset_of to black_magic
Guiorgy Aug 6, 2024
b46f6d5
statically assert that template types passed to Crow are a subset of …
Guiorgy Aug 6, 2024
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2 changes: 2 additions & 0 deletions include/crow/app.h
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Original file line number Diff line number Diff line change
Expand Up @@ -708,6 +708,8 @@ namespace crow
template<typename... Ts>
std::tuple<Middlewares...> make_middleware_tuple(Ts&&... ts)
{
static_assert(black_magic::type_pack<Middlewares...>::template is_superset_of<Ts...>::value, "Constructor argument types must be a subset of the Crow template types");

auto fwd = std::forward_as_tuple((ts)...);
return std::make_tuple(
std::forward<Middlewares>(
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26 changes: 26 additions & 0 deletions include/crow/utility.h
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Original file line number Diff line number Diff line change
Expand Up @@ -453,6 +453,32 @@ namespace crow
struct contains<Tp> : std::false_type
{};

template<typename Tp, typename... List>
struct contains_decayed : std::true_type
{};

template<typename Tp, typename Head, typename... Rest>
struct contains_decayed<Tp, Head, Rest...> :
std::conditional<std::is_same<typename std::decay<Tp>::type, typename std::decay<Head>::type>::value, std::true_type, contains_decayed<Tp, Rest...>>::type
{};

template<typename Tp>
struct contains_decayed<Tp> : std::false_type
{};

template<typename... Tsuper>
struct type_pack
{
template<typename... Tsub>
struct is_superset_of : std::true_type
{};

template<typename T, typename... Tsub>
struct is_superset_of<T, Tsub...> :
std::conditional<contains_decayed<T, Tsuper...>::value, is_superset_of<Tsub...>, std::false_type>::type
{};
};

template<typename T>
struct empty_context
{};
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