[/
 / Copyright (c) 2003-2019 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:Handler Handlers]

A handler must meet the requirements of `MoveConstructible` types (C++Std
[moveconstructible]).

In the table below, `X` denotes a handler class, `h` denotes a value of `X`,
`p` denotes a pointer to a block of allocated memory of type `void*`, `s`
denotes the size for a block of allocated memory, and `f` denotes a function
object taking no arguments.

[table Handler requirements
  [[expression] [return type] [assertion/note\npre/post-conditions]]
  [
    [``
      using boost::asio::asio_handler_allocate;
      asio_handler_allocate(s, &h);
    ``]
    [`void*`]
    [
      Returns a pointer to a block of memory of size `s`. The pointer must
      satisfy the same alignment requirements as a pointer returned by
      `::operator new()`. Throws `bad_alloc` on failure.\n\n The
      `asio_handler_allocate()` function is located using argument-dependent
      lookup. The function `boost::asio::asio_handler_allocate()` serves as a
      default if no user-supplied function is available.
    ]
  ]
  [
    [``
      using boost::asio::asio_handler_deallocate;
      asio_handler_deallocate(p, s, &h);
    ``]
    []
    [
      Frees a block of memory associated with a pointer `p`, of at least size
      `s`, that was previously allocated using `asio_handler_allocate()`.\n\n The
      `asio_handler_deallocate()` function is located using argument-dependent
      lookup. The function `boost::asio::asio_handler_deallocate()` serves as a
      default if no user-supplied function is available.
    ]
  ]
  [
    [``
      using boost::asio::asio_handler_invoke;
      asio_handler_invoke(f, &h);
    ``]
    []
    [
      Causes the function object `f` to be executed as if by calling `f()`.\n\n
      The `asio_handler_invoke()` function is located using argument-dependent
      lookup. The function `boost::asio::asio_handler_invoke()` serves as a
      default if no user-supplied function is available.
    ]
  ]
]

[endsect]