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Update to current std::optional wording
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Update the wording, and reference implementation, to the current draft standard
std::optional synopsis and wording.
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@steve-downey
steve-downey committed Dec 29, 2023
1 parent 2e8d5e6 commit bc6a4bf
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110 changes: 51 additions & 59 deletions papers/optional-ref.md
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Original file line number Diff line number Diff line change
Expand Up @@ -181,17 +181,16 @@ Modify 22.5 Optional Objects
add
```cpp
Class template optional[optional.optional_ref]
General[optional.optional_ref.general]
## Class template optional [optional.optional_ref]
### General [optional.optional_ref.general]
``` C++
namespace std {
namespace std {
template<class T>
class optional<T&> {
public:
using value_type = T;
[optional_ref.ctor], constructors
// [optional_ref.ctor], constructors
constexpr optional() noexcept;
constexpr optional(nullopt_t) noexcept;
constexpr optional(const optional&) noexcept;
Expand All @@ -201,10 +200,10 @@ namespace std {
template <class U>
constexpr explicit optional(const optional<U>& rhs) noexcept;
[optional_ref.dtor], destructor
// [optional_ref.dtor], destructor
constexpr ~optional();
[optional_ref.assign], assignment
// [optional_ref.assign], assignment
constexpr optional& operator=(nullopt_t) noexcept;
constexpr optional& operator=(const optional&);
constexpr optional& operator=(optional&&) noexcept(/* see below */);
Expand All @@ -215,54 +214,47 @@ namespace std {
template <class U>
constexpr optional& operator=(optional<U>&&);
[optional_ref.swap], swap
// [optional_ref.swap], swap
constexpr void swap(optional&) noexcept(/* see below */);
[optional_ref.observe], observers
// [optional_ref.observe], observers
constexpr T* operator->() const noexcept;
constexpr T& operator*() const& noexcept;
constexpr T&& operator*() const&& noexcept;
constexpr explicit operator bool() const noexcept;
constexpr bool has_value() const noexcept;
constexpr T& value() const&;
constexpr T&& value() const&&;
template <class U>
constexpr T value_or(U&&) const&;
[optional_ref.monadic], monadic operations
template <class F>
constexpr auto and_then(F&& f) &;
template <class F>
constexpr auto and_then(F&& f) &&;
template <class F>
constexpr auto and_then(F&& f) const&;
template <class F>
constexpr auto and_then(F&& f) const&&;
template <class F>
constexpr auto transform(F&& f) &;
template <class F>
constexpr auto transform(F&& f) &&;
template <class F>
constexpr auto transform(F&& f) const&;
template <class F>
constexpr auto transform(F&& f) const&&;
template <class F>
constexpr optional or_else(F&& f) &&;
template <class F>
constexpr optional or_else(F&& f) const&;
[optional_ref.mod], modifiers
constexpr const T& value() const &; // freestanding-deleted
constexpr T& value() &; // freestanding-deleted
constexpr T&& value() &&; // freestanding-deleted
constexpr const T&& value() const &&; // freestanding-deleted
template <class U> constexpr T value_or(U&&) const&;
template <class U> constexpr T value_or(U&&) &&;
// [optional_ref.monadic], monadic operations
template <class F> constexpr auto and_then(F&& f) &;
template <class F> constexpr auto and_then(F&& f) &&;
template <class F> constexpr auto and_then(F&& f) const&;
template <class F> constexpr auto and_then(F&& f) const&&;
template <class F> constexpr auto transform(F&& f) &;
template <class F> constexpr auto transform(F&& f) &&;
template <class F> constexpr auto transform(F&& f) const&;
template <class F> constexpr auto transform(F&& f) const&&;
template <class F> constexpr optional or_else(F&& f) &&;
template <class F> constexpr optional or_else(F&& f) const&;
// [optional_ref.mod], modifiers
constexpr void reset() noexcept;
private:
T *val; // exposition only
};
```

Constructors[optional\_ref.ctor]
#### Constructors [optional\_ref.ctor]

```cpp
constexpr optional() noexcept;

constexpr optional(nullopt\_t) noexcept;
constexpr optional(nullopt_t) noexcept;
```
[1]{.pnum} *Postconditions*: `*this` does not contain a value.
Expand Down Expand Up @@ -290,45 +282,45 @@ constexpr optional(optional&&) noexcept;
[5]{.pnum} *Remarks*: The constructor is trivial.
```cpp
template<class U = T>
constexpr optional(U&&);
template<class U = T>
constexpr optional(U&&);
```
[3]{.pnum} *Constraints*:
[6]{.pnum} *Constraints*:

[3.1]{.pnum} -- `!is-optional<decay_t<U>>::value is true`
[6.1]{.pnum} `!is-optional<decay_t<U>>::value is true`

[3]{.pnum} *Mandates*:
[7]{.pnum} *Mandates*:

[3.1]{.pnum} -- `std::is_constructible_v<std::add_lvalue_reference_t<T>, U>`;
[7.1]{.pnum} -- `std::is_constructible_v<std::add_lvalue_reference_t<T>, U>`;

[3.1]{.pnum} -- `std::is_lvalue_reference_v<U>`
[7.1]{.pnum} -- `std::is_lvalue_reference_v<U>`

[3]{.pnum} *Effects*: Initializes `val` with the address of u
[8]{.pnum} *Effects*: Initializes `val` with the address of u

[4]{.pnum} *Postconditions*: `this->has_value() == true`.
[9]{.pnum} *Postconditions*: `this->has_value() == true`.

```cpp
template <class U>
constexpr explicit optional(const optional<U>& rhs) noexcept;
template <class U>
constexpr explicit optional(const optional<U>& rhs) noexcept;
```
[3]{.pnum} *Constraints*:
[10]{.pnum} *Constraints*:
[3.1]{.pnum} -- `!is-optional<decay_t<U>>::value is true`
[10.1]{.pnum} `!is-optional<decay_t<U>>::value is true`
[3]{.pnum} *Mandates*:
[11]{.pnum} *Mandates*:
[3.1]{.pnum} -- `std::is_constructible_v<std::add_lvalue_reference_t<T>, U>`;
[11.1]{.pnum} -- `std::is_constructible_v<std::add_lvalue_reference_t<T>, U>`;
[3.1]{.pnum} -- `std::is_lvalue_reference<U>::value`
[11.1]{.pnum} -- `std::is_lvalue_reference<U>::value`
[3]{.pnum} *Effects*:
[12]{.pnum} *Effects*:
Destructor [optional_ref.dtor]
#### Destructor [optional_ref.dtor]
```cpp
constexpr ~optional();
constexpr ~optional();
```
[5]{.pnum} *Remarks*: The destructor is trivial.
[13]{.pnum} *Remarks*: The destructor is trivial.



Expand Down
14 changes: 13 additions & 1 deletion src/smd/optional/optional.h
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Original file line number Diff line number Diff line change
Expand Up @@ -1023,7 +1023,19 @@ class optional<T&> {
throw bad_optional_access();
}

constexpr T&& value() const&& {
constexpr T& value() & {
if (has_value())
return *value_;
throw bad_optional_access();
}

constexpr T&& value() && {
if (has_value())
return *value_;
throw bad_optional_access();
}

constexpr const T&& value() const&& {
if (has_value())
return *value_;
throw bad_optional_access();
Expand Down

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