This component-private metafunction is derived from bsl::true_type if (template parameter) t_SOURCE can be converted to (template parameter) t_DEST without narrowing, and bsl::false_type otherwise. A conversion from pointer or pointer-to-member type to cv bool is considered narrowing even if the compiler does not implement P1957R2 (which was adopted as a DR); however, on compilers that do not implement P1957R2, we do not have the ability to check whether a user-defined conversion sequence to cv bool would use a narrowing standard conversion, so on those compilers, we permit conversion to a t_DEST that is cv bool only if t_SOURCE is also cv bool, and not when t_SOURCE is a class type. This behavior is not expected to pose a problem for users migrating from bdlb::Variant, because that class does not support implicit conversions from an argument type to an alternative type.
Declared in <bslstl_variant.h>
template<
class t_DEST,
class t_SOURCE>
struct Variant_ConvertsWithoutNarrowing<t_DEST, t_SOURCE, bsl::void_t<decltype(Variant_ArrayHelper<t_DEST>{{std::declval<t_SOURCE>()}})>>
: bsl::integral_constant<bool, !(!Variant_CheckForP1957R2<bool>::value && bsl::is_same<bool, typename bsl::remove_cvref<t_DEST>::type>::value && !bsl::is_same<bool, typename bsl::remove_cvref<t_SOURCE>::type>::value)>| Name | Description |
|---|---|
bsl::integral_constant<bool, !(!Variant_CheckForP1957R2<bool>::value && bsl::is_same<bool, typename bsl::remove_cvref<t_DEST>::type>::value && !bsl::is_same<bool, typename bsl::remove_cvref<t_SOURCE>::type>::value)> | Metafunction representing a compile-time constant of the specified (template parameter) t_TYPE with the specified (template parameter) t_VALUE. |
| Name | Description |
|---|---|
type | Alias for this integral_constant specialization. |
value_type |
| Name | Description |
|---|---|
operator() | Return a copy of the template argument t_VALUE. |
operator value_type |
| Name |
|---|
value |