Handle service requirements

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### Handle service requirements

A handle service must meet the requirements for an I/O object service, as well as the additional requirements listed below.

In the table below, `X` denotes a handle service class, `a` denotes a value of type `X`, `b` denotes a value of type `X::implementation_type`, `n` denotes a value of type `X::native_type`, `ec` denotes a value of type `error_code`, and `u` and `v` denote identifiers.

Table 14. HandleService requirements

expression | return type | assertion/note pre/post-condition
--- | --- | ---
`X::native_type` |  | The implementation-defined native representation of a handle. Must satisfy the requirements of `CopyConstructible` types (C++ Std, 20.1.3), and the requirements of `Assignable` types (C++ Std, 23.1).
`a.construct(b);` |  | From IoObjectService requirements. post: `!a.is_open(b)`.
`a.destroy(b);` |  | From IoObjectService requirements. Implicitly cancels asynchronous operations, as if by calling `a.close(b, ec)`.

    a.assign(b, n, ec);

`error_code`

pre: `!a.is_open(b)`.
post: `!!ec || a.is_open(b)`.

    a.is_open(b);

`bool`

    const X& u = a;
    const X::implementation_type& v = b;
    u.is_open(v);

`bool`

    a.close(b, ec);

`error_code`

If `a.is_open()` is true, causes any outstanding asynchronous operations to complete as soon as possible. Handlers for cancelled operations shall be passed the error code `error::operation_aborted`.
post: `!a.is_open(b)`.

    a.native(b);

`X::native_type`

    a.cancel(b, ec);

`error_code`

pre: `a.is_open(b)`.
Causes any outstanding asynchronous operations to complete as soon as possible. Handlers for cancelled operations shall be passed the error code `error::operation_aborted`.