std::experi...::value_type(3)

💖 std::experi...::value_type(3) 💖

okay so this is straight from the C++ Standard Libary manual, and the main character is std::experimental::ranges::value_type ✨

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🌸 NAME 🌸

std::experimental::ranges::value_type — std::experimental::ranges::value_type

yes bestie, that’s the same name twice; the manpage said it like that and I’m not gonna pretend otherwise 💅

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🦋 Synopsis 🦋

Defined in header <experimental/ranges/iterator>
template< class I >                                          (1)
struct value_type {};
template< class T >                                          (2)
struct value_type<T*>;
template< class I >

    requires std::is_array<I>::value                         (3)

struct value_type<I> : value_type<std::decay_t<I>> {};
template< class T >                                          (4)
struct value_type<const T> : value_type<std::decay_t<T>> {};
template< class T >

    requires requires { typename T::value_type; }            (5)

struct value_type<T>;
template< class T >

    requires requires { typename T::element_type; }          (6)

struct value_type<T>;

So what’s the vibe? It computes the associated value type of the type I, if any. And yes, users may specialize value_type for a program-defined type 🫶

Here’s the numbered rundown, no cap:

• (1) — the primary template is an empty struct. Literally struct value_type {}; and nothing else.
• (2) — specialization for pointers. If T is an object type, it provides a member type type equal to std::remove_cv_t<T>. Otherwise, there is no member type.
• (3) — specialization for array types. The code is struct value_type<I> : value_type<std::decay_t<I>> {}; under requires std::is_array<I>::value.
• (4) — specialization for const-qualified types. The code is struct value_type<const T> : value_type<std::decay_t<T>> {};.
• (5) — specialization for types that define a public and accessible member type value_type. If T::value_type is an object type, it provides a member type type equal to T::value_type. Otherwise, there is no member type.
• (6) — specialization for types that define a public and accessible member type element_type (e.g., std::shared_ptr). If T::element_type is an object type, it provides a member type type equal to std::remove_cv_t<typename T::element_type>. Otherwise, there is no member type.

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🦋 Notes 🦋

⚠️ bestie, listen: if a type contains both a value_type member and a element_type member, then the specializations (5) and (6) are ambiguous. That’s the drama.

value_type is intended for use with Readable types such as iterators. It is not intended for use with ranges.

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🍓 Example 🍓

🚧 This section is incomplete Reason: no example

not me showing up with an empty example section 💀 but that’s literally what the page says.

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🌈 See also 🌈

• Readable (concept) — specifies that a type is readable by applying operator *.
• iterator_traits (alias template) — compatibility traits class that collects an iterator’s associated types.

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🎀 Category: 🎀

• * Todo no example

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okay that’s the whole page, bestie 🫶 source/version vibes from http://cppreference.com, dated 2024.06.10, and the footer signature is std::experi...::value_type(3). mwah 💋✨