Completion condition requirements

A completion condition is a function object that is used with the algorithms read, async_read, write, and async_write to determine when the algorithm has completed transferring data.

A type X meets the CompletionCondition requirements if it satisfies the requirements of Destructible (C++Std [destructible]) and MoveConstructible (C++Std [moveconstructible]), as well as the additional requirements listed below.

In the table below, x denotes a value of type X, ec denotes a (possibly const) value of type error_code, and n denotes a (possibly const) value of type size_t.

Table 9. CompletionCondition requirements

expression	return type	assertion/note pre/post-condition
`x(ec, n)`	`size_t`	Let `n` be the total number of bytes transferred by the read or write algorithm so far. Returns the maximum number of bytes to be transferred on the next `read_some`, `async_read_some`, `write_some`, or `async_write_some` operation performed by the algorithm. Returns `0` to indicate that the algorithm is complete.