malloy::mp Namespace Reference

Namespace for metaprogramming utils. More...

Typedefs
template<typename V>
using	unwrap_variant = std::conditional_t<std::variant_size_v<V> == 1, std::variant_alternative_t<0, V>, V>
	Pattern: unwrap_variant<variant<T>> -> T unwrap_variant<variant<T, ...> -> std::variant<T, ...>.
template<typename V>
using	body_type = unwrap_variant<V>
	Converts from a variant of possible bodies to the actual body type taken by callbacks.
template<typename F>
using	bodies_for_t = std::invoke_result_t<decltype(&F::body_for), const F*, const typename F::header_type&>
	Resolves the body type used by a filter F.
template<typename Bodies>
using	to_responses = typename decltype(detail::conv_to_resp_helper{std::declval<Bodies>()})::type
	Converts a variant<T...> where T is body to a variant<response<T>...>.
template<typename Filter>
using	filter_resp_t = unwrap_variant<to_responses<bodies_for_t<Filter>>>
	Resolves to the type that must be taken in callbacks handling responses for Filter.

Detailed Description

Namespace for metaprogramming utils.

Typedef Documentation

unwrap_variant

template<typename V>

using malloy::mp::unwrap_variant = std::conditional_t<std::variant_size_v<V> == 1, std::variant_alternative_t<0, V>, V>

Pattern: unwrap_variant<variant<T>> -> T unwrap_variant<variant<T, ...> -> std::variant<T, ...>.

i.e. If it is a 1 element it just returns that type, otherwise the entire variant type.