This component-private metafunction provides the implementation of bsl::variant_alternative.
Declared in <bslstl_variant.h>
template<
std::size_t t_INDEX,
class t_HEAD = BSLSTL_VARIANT_NOT_A_TYPE,
class... t_TAIL>
struct Variant_VariantAlternativeImpl
: Variant_VariantAlternativeImpl<t_INDEX - 1, t_TAIL...>It recursively strips one type from the front of (template parameters) t_HEAD, t_TAIL... for each decrement of (template parameter) t_INDEX until t_INDEX reaches 0, at which point the resulting t_HEAD is the alternative type.
| Name | Description |
|---|---|
Variant_VariantAlternativeImpl<t_INDEX - 1, t_TAIL...> | This component-private metafunction provides the implementation of bsl::variant_alternative. |
| Name | Description |
|---|---|
Variant_VariantAlternativeImpl<0, BSLSTL_VARIANT_NOT_A_TYPE> | This explicit specialization handles the case of an empty alternative list queried at index 0. No member typedef is provided. |
Variant_VariantAlternativeImpl<t_INDEX, BSLSTL_VARIANT_NOT_A_TYPE> | This partial specialization is used when the list of alternatives is exhausted before t_INDEX reaches 0, i.e., t_INDEX is out of range. |
Variant_VariantAlternativeImpl<0, t_HEAD, t_TAIL...> | This partial specialization is the base case of the recursion, reached when t_INDEX is 0; it provides the member typedef type equal to t_HEAD. |
| Name | Description |
|---|---|
Variant_VariantAlternativeImpl | This component-private metafunction provides the implementation of bsl::variant_alternative. |
variant_alternative<t_INDEX, variant<t_HEAD, t_TAIL...>> | Compute the alternative type at index t_INDEX of a bsl::variant. |