I/O object service requirements

An I/O object service must meet the requirements for a service, as well as the requirements listed below.

In the table below, X denotes an I/O object service class, a and ao denote values of type X, b and c denote values of type X::implementation_type, and u denotes an identifier.

Table 23. IoObjectService requirements

expression	return type	assertion/note pre/post-condition
`X::implementation_type`
`X::implementation_type u;`		note: `X::implementation_type` has a public default constructor and destructor.
a.construct(b);
a.destroy(b);		note: `destroy()` will only be called on a value that has previously been initialised with `construct()` or `move_construct()`.
a.move_construct(b, c);		note: only required for I/O objects that support movability.
a.move_assign(b, ao, c);		note: only required for I/O objects that support movability.