### 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 21. 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.