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#pragma once
#include <cstddef>
#include <utility>
namespace NYql::NPrivate::NRuntimeDispatch {
template <typename... T>
struct TTypeList {};
template <bool...>
struct TValueList {};
template <size_t N, class F, bool... Values, typename... TArgs>
decltype(auto) RuntimeDispatchOneElement(F&& func,
TValueList<Values...>,
bool boolArg,
TArgs&&... restArgs) {
if (boolArg) {
return RuntimeDispatchImpl<N - 1, F>(
std::forward<F>(func),
TValueList<Values..., true>(), std::forward<TArgs>(restArgs)...);
} else {
return RuntimeDispatchImpl<N - 1, F>(
std::forward<F>(func),
TValueList<Values..., false>(), std::forward<TArgs>(restArgs)...);
}
}
template <size_t N, class F, bool... Values, typename... TArgs>
decltype(auto) RuntimeDispatchImpl(F&& func,
TValueList<Values...>, TArgs&&... args) {
static_assert(sizeof...(TArgs) >= N,
"RuntimeDispatch requires at least N arguments");
if constexpr (N == 0) {
return func.template operator()<Values...>(std::forward<TArgs>(args)...);
} else {
return RuntimeDispatchOneElement<N, F>(
std::forward<F>(func), TValueList<Values...>(),
std::forward<TArgs>(args)...);
}
}
template <size_t N, class F, typename... TArgs>
auto RuntimeDispatch(F&& func, TArgs&&... args) {
return RuntimeDispatchImpl<N, F>(std::forward<F>(func), TValueList<>(), std::forward<TArgs>(args)...);
}
} // namespace NYql::NPrivate::NRuntimeDispatch
#define YQL_PRIVATE_WRAP_LAMBDA_FOR_FUNCTION(call, returnType) \
[]<bool... Bs>(auto&&... args) -> returnType { \
return call<Bs...>(std::forward<decltype(args)>(args)...); \
}
#define YQL_PRIVATE_WRAP_LAMBDA_FOR_NEW(constructor, returnType) \
[]<bool... Bs>(auto&&... args) -> returnType { \
return new constructor<Bs...>(std::forward<decltype(args)>(args)...); \
}
// Dispatches at runtime to a template function based on N leading arguments.
// Avoids the if/else branch hell. Example:
//
// Before:
// if (a && b) {
// return Foo<true, true>(x);
// } else if (a) {
// return Foo<true, false>(x);
// } else if (b) {
// return Foo<false, true>(x);
// } else {
// return Foo<false, false>(x);
// }
//
// After:
// return YQL_RUNTIME_DISPATCH(Foo, 2, a, b, x);
#define YQL_RUNTIME_DISPATCH(funcName, N, ...) \
(NYql::NPrivate::NRuntimeDispatch::RuntimeDispatch<(N)>(YQL_PRIVATE_WRAP_LAMBDA_FOR_FUNCTION(funcName, decltype(auto)), __VA_ARGS__))
// Same as YQL_RUNTIME_DISPATCH, but for the new operator.
// Example:
//
// Before:
// if (a && b) {
// return new Foo<true, true>(x);
// } else if (a) {
// return new Foo<true, false>(x);
// } else if (b) {
// return new Foo<false, true>(x);
// } else {
// return new Foo<false, false>(x);
// }
//
// After:
// return YQL_RUNTIME_DISPATCH_NEW(Base, Foo, 2, a, b, x);
#define YQL_RUNTIME_DISPATCH_NEW(returnType, constructor, N, ...) \
(NYql::NPrivate::NRuntimeDispatch::RuntimeDispatch<(N)>(YQL_PRIVATE_WRAP_LAMBDA_FOR_NEW(constructor, returnType), __VA_ARGS__))
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