常に右側を保持するモノイド
(math/monoid/hold.hpp)

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• Last update: 2025-06-06 16:34:35+09:00
• Include: #include "math/monoid/hold.hpp"

Depends on

• type_traits/io.hpp

Verified with

• verify/unit_test/monoid.test.cpp
• verify/yosupo_ds/ds_ordered_set_max_right.test.cpp

Code

#ifndef KK2_MATH_MONOID_HOLD_HPP
#define KK2_MATH_MONOID_HOLD_HPP 1

#include "../../type_traits/io.hpp"

namespace kk2 {

namespace monoid {

/**
 * @brief 常に右側を保持するモノイド
 */
template <class S> struct Hold {
    static constexpr bool commutative = true;
    using M = Hold;

    S a;
    bool is_unit;

    Hold() : is_unit(true) {}
    Hold(S a_) : a(a_), is_unit(false) {}
    operator S() const { return a; }
    inline static M op(M l, M r) { return r.is_unit ? l : r; }
    inline static M unit() { return M(); }

    bool operator==(const M &rhs) const {
        return is_unit == rhs.is_unit and (is_unit or a == rhs.a);
    }

    bool operator!=(const M &rhs) const {
        return is_unit != rhs.is_unit or (!is_unit and a != rhs.a);
    }

    template <class OStream, is_ostream_t<OStream> * = nullptr>
    friend OStream &operator<<(OStream &os, const M &x) {
        if (x.is_unit) os << "unit";
        else os << x.a;
        return os;
    }

    template <class IStream, is_istream_t<IStream> * = nullptr>
    friend IStream &operator>>(IStream &is, M &x) {
        is >> x.a;
        x.is_unit = false;
        return is;
    }
};

} // namespace monoid

} // namespace kk2

#endif // KK2_MATH_MONOID_HOLD_HPP

Traceback (most recent call last):
  File "/opt/hostedtoolcache/Python/3.12.0/x64/lib/python3.12/site-packages/onlinejudge_verify/documentation/build.py", line 71, in _render_source_code_stat
    bundled_code = language.bundle(stat.path, basedir=basedir, options={'include_paths': [basedir]}).decode()
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/hostedtoolcache/Python/3.12.0/x64/lib/python3.12/site-packages/onlinejudge_verify/languages/cplusplus.py", line 187, in bundle
    bundler.update(path)
  File "/opt/hostedtoolcache/Python/3.12.0/x64/lib/python3.12/site-packages/onlinejudge_verify/languages/cplusplus_bundle.py", line 401, in update
    self.update(self._resolve(pathlib.Path(included), included_from=path))
  File "/opt/hostedtoolcache/Python/3.12.0/x64/lib/python3.12/site-packages/onlinejudge_verify/languages/cplusplus_bundle.py", line 312, in update
    raise BundleErrorAt(path, i + 1, "#pragma once found in a non-first line")
onlinejudge_verify.languages.cplusplus_bundle.BundleErrorAt: type_traits/io.hpp: line 4: #pragma once found in a non-first line

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