From Jason Turner

[time.cal.ym]

C++17 → C++20 6.4 KB 222 lines
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tmp/tmppp6emfgq/{from.md → to.md} RENAMED
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+ ### Class `year_month` <a id="time.cal.ym">[[time.cal.ym]]</a>
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+
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+ #### Overview <a id="time.cal.ym.overview">[[time.cal.ym.overview]]</a>
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+
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+ ``` cpp
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+ namespace std::chrono {
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+ class year_month {
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+ chrono::year y_; // exposition only
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+ chrono::month m_; // exposition only
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+
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+ public:
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+ year_month() = default;
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+ constexpr year_month(const chrono::year& y, const chrono::month& m) noexcept;
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+
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+ constexpr chrono::year year() const noexcept;
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+ constexpr chrono::month month() const noexcept;
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+
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+ constexpr year_month& operator+=(const months& dm) noexcept;
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+ constexpr year_month& operator-=(const months& dm) noexcept;
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+ constexpr year_month& operator+=(const years& dy) noexcept;
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+ constexpr year_month& operator-=(const years& dy) noexcept;
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+
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+ constexpr bool ok() const noexcept;
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+ };
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+ }
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+ ```
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+
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+ `year_month` represents a specific month of a specific year, but with an
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+ unspecified day. `year_month` is a field-based time point with a
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+ resolution of `months`. `year_month` meets the *Cpp17EqualityComparable*
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+ ([[cpp17.equalitycomparable]]) and *Cpp17LessThanComparable* (
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+ [[cpp17.lessthancomparable]]) requirements.
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+
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+ `year_month` is a trivially copyable and standard-layout class type.
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+
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+ #### Member functions <a id="time.cal.ym.members">[[time.cal.ym.members]]</a>
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+
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+ ``` cpp
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+ constexpr year_month(const chrono::year& y, const chrono::month& m) noexcept;
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+ ```
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+
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+ *Effects:* Initializes `y_` with `y`, and `m_` with `m`.
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+
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+ ``` cpp
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+ constexpr chrono::year year() const noexcept;
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+ ```
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+
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+ *Returns:* `y_`.
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+
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+ ``` cpp
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+ constexpr chrono::month month() const noexcept;
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+ ```
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+
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+ *Returns:* `m_`.
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+
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+ ``` cpp
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+ constexpr year_month& operator+=(const months& dm) noexcept;
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+ ```
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+
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+ *Constraints:* If the argument supplied by the caller for the `months`
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+ parameter is convertible to `years`, its implicit conversion sequence to
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+ `years` is worse than its implicit conversion sequence to `months`
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+ [[over.ics.rank]].
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+
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+ *Effects:* `*this = *this + dm`.
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+
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+ *Returns:* `*this`.
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+
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+ ``` cpp
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+ constexpr year_month& operator-=(const months& dm) noexcept;
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+ ```
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+
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+ *Constraints:* If the argument supplied by the caller for the `months`
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+ parameter is convertible to `years`, its implicit conversion sequence to
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+ `years` is worse than its implicit conversion sequence to `months`
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+ [[over.ics.rank]].
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+
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+ *Effects:* `*this = *this - dm`.
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+
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+ *Returns:* `*this`.
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+
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+ ``` cpp
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+ constexpr year_month& operator+=(const years& dy) noexcept;
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+ ```
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+
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+ *Effects:* `*this = *this + dy`.
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+
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+ *Returns:* `*this`.
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+
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+ ``` cpp
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+ constexpr year_month& operator-=(const years& dy) noexcept;
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+ ```
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+
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+ *Effects:* `*this = *this - dy`.
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+
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+ *Returns:* `*this`.
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+
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+ ``` cpp
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+ constexpr bool ok() const noexcept;
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+ ```
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+
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+ *Returns:* `y_.ok() && m_.ok()`.
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+
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+ #### Non-member functions <a id="time.cal.ym.nonmembers">[[time.cal.ym.nonmembers]]</a>
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+
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+ ``` cpp
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+ constexpr bool operator==(const year_month& x, const year_month& y) noexcept;
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+ ```
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+
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+ *Returns:* `x.year() == y.year() && x.month() == y.month()`.
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+
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+ ``` cpp
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+ constexpr strong_ordering operator<=>(const year_month& x, const year_month& y) noexcept;
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+ ```
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+
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+ *Effects:* Equivalent to:
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+
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+ ``` cpp
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+ if (auto c = x.year() <=> y.year(); c != 0) return c;
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+ return x.month() <=> y.month();
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+ ```
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+
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+ ``` cpp
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+ constexpr year_month operator+(const year_month& ym, const months& dm) noexcept;
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+ ```
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+
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+ *Constraints:* If the argument supplied by the caller for the `months`
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+ parameter is convertible to `years`, its implicit conversion sequence to
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+ `years` is worse than its implicit conversion sequence to `months`
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+ [[over.ics.rank]].
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+
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+ *Returns:* A `year_month` value `z` such that `z.ok() && z - ym == dm`
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+ is `true`.
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+
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+ *Complexity:* 𝑂(1) with respect to the value of `dm`.
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+
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+ ``` cpp
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+ constexpr year_month operator+(const months& dm, const year_month& ym) noexcept;
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+ ```
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+
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+ *Constraints:* If the argument supplied by the caller for the `months`
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+ parameter is convertible to `years`, its implicit conversion sequence to
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+ `years` is worse than its implicit conversion sequence to `months`
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+ [[over.ics.rank]].
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+
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+ *Returns:* `ym + dm`.
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+
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+ ``` cpp
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+ constexpr year_month operator-(const year_month& ym, const months& dm) noexcept;
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+ ```
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+
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+ *Constraints:* If the argument supplied by the caller for the `months`
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+ parameter is convertible to `years`, its implicit conversion sequence to
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+ `years` is worse than its implicit conversion sequence to `months`
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+ [[over.ics.rank]].
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+
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+ *Returns:* `ym + -dm`.
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+
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+ ``` cpp
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+ constexpr months operator-(const year_month& x, const year_month& y) noexcept;
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+ ```
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+
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+ *Returns:*
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+
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+ ``` cpp
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+ x.year() - y.year() + months{static_cast<int>(unsigned{x.month()}) -
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+ static_cast<int>(unsigned{y.month()})}
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+ ```
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+
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+ ``` cpp
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+ constexpr year_month operator+(const year_month& ym, const years& dy) noexcept;
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+ ```
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+
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+ *Returns:* `(ym.year() + dy) / ym.month()`.
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+
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+ ``` cpp
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+ constexpr year_month operator+(const years& dy, const year_month& ym) noexcept;
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+ ```
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+
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+ *Returns:* `ym + dy`.
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+
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+ ``` cpp
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+ constexpr year_month operator-(const year_month& ym, const years& dy) noexcept;
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+ ```
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+
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+ *Returns:* `ym + -dy`.
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+
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+ ``` cpp
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+ template<class charT, class traits>
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+ basic_ostream<charT, traits>&
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+ operator<<(basic_ostream<charT, traits>& os, const year_month& ym);
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+ ```
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+
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+ *Effects:* Equivalent to:
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+
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+ ``` cpp
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+ return os << format(os.getloc(), STATICALLY-WIDEN<charT>("{}/{}"),
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+ ym.year(), ym.month());
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+ ```
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+
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+ ``` cpp
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+ template<class charT, class traits, class Alloc = allocator<charT>>
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+ basic_istream<charT, traits>&
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+ from_stream(basic_istream<charT, traits>& is, const charT* fmt,
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+ year_month& ym, basic_string<charT, traits, Alloc>* abbrev = nullptr,
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+ minutes* offset = nullptr);
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+ ```
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+
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+ *Effects:* Attempts to parse the input stream `is` into the `year_month`
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+ `ym` using the format flags given in the NTCTS `fmt` as specified in
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+ [[time.parse]]. If the parse fails to decode a valid `year_month`,
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+ `is.setstate(ios_base::failbit)` is called and `ym` is not modified. If
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+ `%Z` is used and successfully parsed, that value will be assigned to
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+ `*abbrev` if `abbrev` is non-null. If `%z` (or a modified variant) is
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+ used and successfully parsed, that value will be assigned to `*offset`
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+ if `offset` is non-null.
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+
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+ *Returns:* `is`.
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+