Document when types have OS-dependent sizes

src/libstd/net/addr.rs

@@ -28,6 +28,9 @@ use slice;
 /// as possibly some version-dependent additional information. See [`SocketAddrV4`]'s and
 /// [`SocketAddrV6`]'s respective documentation for more details.
 ///
+/// The size of a `SocketAddr` instance may vary depending on the target operating
+/// system.
+///
 /// [IP address]: ../../std/net/enum.IpAddr.html
 /// [`SocketAddrV4`]: ../../std/net/struct.SocketAddrV4.html
 /// [`SocketAddrV6`]: ../../std/net/struct.SocketAddrV6.html
@@ -61,6 +64,9 @@ pub enum SocketAddr {
 ///
 /// See [`SocketAddr`] for a type encompassing both IPv4 and IPv6 socket addresses.
 ///
+/// The size of a `SocketAddrV4` struct may vary depending on the target operating
+/// system.
+///
 /// [IETF RFC 793]: https://tools.ietf.org/html/rfc793
 /// [IPv4 address]: ../../std/net/struct.Ipv4Addr.html
 /// [`SocketAddr`]: ../../std/net/enum.SocketAddr.html
@@ -88,6 +94,9 @@ pub struct SocketAddrV4 { inner: c::sockaddr_in }
 ///
 /// See [`SocketAddr`] for a type encompassing both IPv4 and IPv6 socket addresses.
 ///
+/// The size of a `SocketAddrV6` struct may vary depending on the target operating
+/// system.
+///
 /// [IETF RFC 2553, Section 3.3]: https://tools.ietf.org/html/rfc2553#section-3.3
 /// [IPv6 address]: ../../std/net/struct.Ipv6Addr.html
 /// [`SocketAddr`]: ../../std/net/enum.SocketAddr.html

src/libstd/net/ip.rs

@@ -26,6 +26,9 @@ use sys_common::{AsInner, FromInner};
 /// This enum can contain either an [`Ipv4Addr`] or an [`Ipv6Addr`], see their
 /// respective documentation for more details.
 ///
+/// The size of an `IpAddr` instance may vary depending on the target operating
+/// system.
+///
 /// [`Ipv4Addr`]: ../../std/net/struct.Ipv4Addr.html
 /// [`Ipv6Addr`]: ../../std/net/struct.Ipv6Addr.html
 ///
@@ -61,6 +64,9 @@ pub enum IpAddr {
 ///
 /// See [`IpAddr`] for a type encompassing both IPv4 and IPv6 addresses.
 ///
+/// The size of an `Ipv4Addr` struct may vary depending on the target operating
+/// system.
+///
 /// [IETF RFC 791]: https://tools.ietf.org/html/rfc791
 /// [`IpAddr`]: ../../std/net/enum.IpAddr.html
 ///
@@ -93,6 +99,9 @@ pub struct Ipv4Addr {
 ///
 /// See [`IpAddr`] for a type encompassing both IPv4 and IPv6 addresses.
 ///
+/// The size of an `Ipv6Addr` struct may vary depending on the target operating
+/// system.
+///
 /// [IETF RFC 4291]: https://tools.ietf.org/html/rfc4291
 /// [`IpAddr`]: ../../std/net/enum.IpAddr.html
 ///

src/libstd/time.rs

@@ -49,6 +49,9 @@ pub use core::time::Duration;
 /// allows measuring the duration between two instants (or comparing two
 /// instants).
 ///
+/// The size of an `Instant` struct may vary depending on the target operating
+/// system.
+///
 /// Example:
 ///
 /// ```no_run
@@ -88,6 +91,9 @@ pub struct Instant(time::Instant);
 /// fixed point in time, a `SystemTime` can be converted to a human-readable time,
 /// or perhaps some other string representation.
 ///
+/// The size of a `SystemTime` struct may vary depending on the target operating
+/// system.
+///
 /// [`Instant`]: ../../std/time/struct.Instant.html
 /// [`Result`]: ../../std/result/enum.Result.html
 /// [`Duration`]: ../../std/time/struct.Duration.html