21 Metaprogramming library [meta]

Let CharT be ranges​::​range_value_t<R>.

Mandates: CharT is one of char, wchar_t, char8_t, char16_t, char32_t.

Let V be the pack of values of type CharT whose elements are the corresponding elements of r, except that if r refers to a string literal object, then V does not include the trailing null terminator of r.

Let P be the template parameter object ([temp.param]) of type const CharT[sizeof...(V) + 1] initialized with {V..., CharT()}.

Returns: ^^P.

Let T be ranges​::​range_value_t<R>.

Mandates: T is a structural type ([temp.param]), is_constructible_v<T, ranges​::​range_reference_t<R>> is true, and is_copy_constructible_v<T> is true.

Let V be the pack of values of type info of the same size as r, where the $i^{\text{th}}$ element is reflect_constant($\text{e}{}_i$), where $\text{e}{}_i$ is the $i^{\text{th}}$ element of r.

Let P be

• (11.1)
  If sizeof...(V) > 0 is true, then the template parameter object ([temp.param]) of type const T[​sizeof...(​V)] initialized with {[:V:]...}.
• (11.2)
  Otherwise, the template parameter object of type const array<T, 0> initialized with {}.

Returns: ^^P.

Throws: meta​::​exception unless reflect_constant(e) is a constant subexpression for every element e of r.

Effects: Equivalent to: return meta::extract<const ranges::range_value_t<R>*>(meta::reflect_constant_string(r));

Effects: Equivalent to: using T = ranges::range_value_t<R>; meta::info array = meta::reflect_constant_array(r); if (meta::is_array_type(meta::type_of(array))) { return span<const T>(meta::extract<const T*>(array), meta::extent(meta::type_of(array))); } else { return span<const T>(); }

Effects: Equivalent to: using U = remove_cvref_t<T>; if constexpr (meta::is_class_type(^^U)) { return addressof(meta::extract<const U&>(meta::reflect_constant(std::forward<T>(t)))); } else { return define_static_array(span(addressof(t), 1)).data(); }