util::has_extracted_type< Extractor, Target, Tuple > Struct Template Reference

Trait holding whether an element in Tuple type contains Target. More...

#include <TupleLookupByTag.h>

Inheritance diagram for util::has_extracted_type< Extractor, Target, Tuple >:

Detailed Description

template<template< typename T, typename...> class Extractor, typename Target, typename Tuple>
struct util::has_extracted_type< Extractor, Target, Tuple >

Trait holding whether an element in Tuple type contains Target.

Template Parameters

Extractor	trait exposing the target type in an element
Target	the target type to be found
Tuple	the tuple-like type to be investigated

See Also

has_extracted_type_v, index_of_extracted_type, count_extracted_types, has_type

Given a tuple-like type Tuple, this trait returns whether there is at least an element type which "contains" the target type Target. For example:

template <typename T>
struct ExtractValueType { using type = typename T::value_type; };

using tuple_t
  = std::tuple<std::vector<float>, std::vector<int>, std::list<int>>;

constexpr bool hasIntegerContainers
  = util::has_extracted_type<ExtractValueType, int, tuple_t>();
constexpr bool hasDoubleContainers
  = util::has_extracted_type<ExtractValueType, double, tuple_t>();

hasIntegerContainers will hold value true, meaning there are two types with int as value_type. Likewise, hasDoubleContainers will be false.

Note

Before C++17, the following construct is invalid: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp} using tuple_t = std::tuple<std::vector<float>, std::vector<int>, std::list<int>>; tuple_t data { { 0.5, 1.5 }, { 0, 2, 4 }, { 1, 3, 5 } }; if (util::has_extracted_type<ExtractValueType, int, tuple_t>()) return util::getByExtractedType<ExtractValueType, int>(data); ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ because util::getByExtractedType<ExtractValueType, double>(data) needs to be compilable, but it is not since it has more than one int extracted types. This is solved in C++17 by the use of a "constexpr if".

Definition at line 377 of file TupleLookupByTag.h.

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The documentation for this struct was generated from the following file:

• TupleLookupByTag.h