Gettable socket option requirements

A type X meets the GettableSocketOption requirements if it satisfies the requirements listed below.

In the table below, a denotes a (possibly const) value of type X, b denotes a value of type X, p denotes a (possibly const) value that meets the Protocol requirements, and s denotes a (possibly const) value of a type that is convertible to size_t and denotes a size in bytes.

Table 20. GettableSocketOption requirements for extensible implementations

expression	type	assertion/note pre/post-conditions
`a.level(p)`	`int`	Returns a value suitable for passing as the level argument to POSIX `getsockopt()` (or equivalent).
`a.name(p)`	`int`	Returns a value suitable for passing as the option_name argument to POSIX `getsockopt()` (or equivalent).
`b.data(p)`	`void*`	Returns a pointer suitable for passing as the option_value argument to POSIX `getsockopt()` (or equivalent).
`a.size(p)`	`size_t`	Returns a value suitable for passing as the option_len argument to POSIX `getsockopt()` (or equivalent), after appropriate integer conversion has been performed.
`b.resize(p,s)`		post: `b.size(p) == s`. Passed the value contained in the option_len argument to POSIX `getsockopt()` (or equivalent) after successful completion of the function. Permitted to throw an exception if the socket option object `b` does not support the specified size.