[/
 / Copyright (c) 2003-2016 Christopher M. Kohlhoff (chris at kohlhoff dot com)
 /
 / Distributed under the Boost Software License, Version 1.0. (See accompanying
 / file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 /]

[section:TimeTraits Time traits requirements]

In the table below, `X` denotes a time traits class for time type `Time`, `t`,
`t1`, and `t2` denote values of type `Time`, and `d` denotes a value of type
`X::duration_type`.

[table TimeTraits requirements
  [[expression] [return type] [assertion/note\npre/post-condition]]
  [
    [`X::time_type`]
    [`Time`]
    [
      Represents an absolute time. Must support default construction, and meet
      the requirements for `CopyConstructible` and `Assignable`.
    ]
  ]
  [
    [`X::duration_type`]
    []
    [
      Represents the difference between two absolute times. Must support
      default construction, and meet the requirements for `CopyConstructible`
      and `Assignable`. A duration can be positive, negative, or zero.
    ]
  ]
  [
    [`X::now();`]
    [`time_type`]
    [
      Returns the current time.
    ]
  ]
  [
    [`X::add(t, d);`]
    [`time_type`]
    [
      Returns a new absolute time resulting from adding the duration `d` to the
      absolute time `t`.
    ]
  ]
  [
    [`X::subtract(t1, t2);`]
    [`duration_type`]
    [
      Returns the duration resulting from subtracting `t2` from `t1`.
    ]
  ]
  [
    [`X::less_than(t1, t2);`]
    [`bool`]
    [
      Returns whether `t1` is to be treated as less than `t2`.
    ]
  ]
  [
    [`X::to_posix_duration(d);`]
    [`date_time::time_duration_type`]
    [
      Returns the `date_time::time_duration_type` value that most closely
      represents the duration `d`.
    ]
  ]
]

[endsect]