[/
 / Copyright (c) 2003-2025 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:CancellationSlot Cancellation slot requirements]

A type `X` meets the `CancellationSlot` requirements if it satisfies the
requirements of `CopyConstructible` (C++Std [copyconstructible]) and
`Destructible` (C++Std [destructible]), as well as the additional requirements
listed below.

In the table below, `x1` and `x2` denote (possibly const) values of type `X`,
`mx1` denotes an xvalue of type `X`, `H` denotes a type that satisfies
`CancellationHandler`, `h` denotes an xvalue of type `H`, and `u0` to `uN`
denote identifiers.

[table CancellationSlot requirements
  [[expression] [type] [assertion/note[br]pre/post-conditions]]
  [
    [`X u(x1);`]
    []
    [Shall not exit via an exception.[br]
     [br]
     post: `u == x1`.]
  ]
  [
    [`X u(mx1);`]
    []
    [Shall not exit via an exception.[br]
     [br]
     post: `u` equals the prior value of `mx1`.]
  ]
  [
    [`x1 == x2`]
    [`bool`]
    [ Returns `true` only if `x1` and `x2` can be interchanged with identical
     effects.
     [br]
     `operator==` shall be reflexive, symmetric, and transitive, and shall not
     exit via an exception.]
  ]
  [
    [`x1 != x2`]
    [`bool`]
    [Same as `!(x1 == x2)`.]
  ]
  [
    [`x1.is_connected()`]
    [`bool`]
    [Returns `false` only if the slot can never cause the invocation of a
     handler attached to the slot using `assign` or `emplace`.]
  ]
  [
    [`x1.has_handler()`]
    [`bool`]
    [Returns `true` if a handler has been attached to the slot.]
  ]
  [
    [`x1.assign(h)`]
    [`H&`]
    [Destroys the existing handler that is attached to the slot, if any, and
     attaches a move-constructed decay-copy of the handler `h`.[br]
     [br]
     Returns a reference to the newly attached handler.[br]
     [br]
     post: `x1.has_handler() == true`.]
  ]
  [
    [`x1.emplace<H>(u0, ..., uN)`]
    [`H&`]
    [Requires that `is_constructible<H, decltype(u0), ...,
     decltype(u0)>::value` be true.[br]
     [br]
     Destroys the existing handler that is attached to the slot, if any, and
     attaches a handler of type `H` constructed with the specified arguments
     `u0, ..., uN`.[br]
     [br]
     Returns a reference to the newly attached handler.[br]
     [br]
     post: `x1.has_handler() == true`.]
  ]
  [
    [`x1.clear()`]
    []
    [Post: `x1.has_handler() == false`.]
  ]
]

[endsect]
