[time.traits.duration.values]

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template<class Rep>
  struct duration_values {
  public:
    static constexpr Rep zero() noexcept;
    static constexpr Rep min() noexcept;
    static constexpr Rep max() noexcept;
  };

The duration template uses the duration_values trait to construct special values of the duration's representation (Rep).

This is done because the representation can be a class type with behavior that requires some other implementation to return these special values.

In that case, the author of that class type should specialize duration_values to return the indicated values.

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static constexpr Rep zero() noexcept;

Returns: Rep(0).

[Note 1:

Rep(0) is specified instead of Rep() because Rep() can have some other meaning, such as an uninitialized value.

— end note]

Remarks: The value returned shall be the additive identity.

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static constexpr Rep min() noexcept;

Remarks: The value returned shall compare less than or equal to zero().

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static constexpr Rep max() noexcept;

Remarks: The value returned shall compare greater than zero().

30 Time library [time]

30.4 Time-related traits [time.traits]

30.4.2 duration_values [time.traits.duration.values]