Implement AsRawFd/IntoRawFd for RawFd

This is useful to build os abstraction like the nix crate does.
It allows to define functions, which accepts generic arguments
of data structures convertible to RawFd, including RawFd itself.
For example:

  fn write<FD: AsRawFd>(fd: FD, buf: &[u8]) -> Result<usize>

instead of:

  fn write(fd: RawFd, buf: &[u8]) -> Result<usize>
  write(foo.as_raw_fd(), buf);

1 files changed, 15 insertions, 0 deletions

diff --git a/src/libstd/sys/unix/ext/io.rs b/src/libstd/sys/unix/ext/io.rs
index 296235e173d..75aa72e3cff 100644
--- a/src/libstd/sys/unix/ext/io.rs
+++ b/src/libstd/sys/unix/ext/io.rs
@@ -73,6 +73,13 @@ pub trait IntoRawFd {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
+impl AsRawFd for RawFd {
+    fn as_raw_fd(&self) -> RawFd {
+        *self
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
 impl AsRawFd for fs::File {
     fn as_raw_fd(&self) -> RawFd {
         self.as_inner().fd().raw()
@@ -84,6 +91,14 @@ impl FromRawFd for fs::File {
         fs::File::from_inner(sys::fs::File::from_inner(fd))
     }
 }
+
+#[stable(feature = "into_raw_os", since = "1.4.0")]
+impl IntoRawFd for RawFd {
+    fn into_raw_fd(self) -> RawFd {
+        self
+    }
+}
+
 #[stable(feature = "into_raw_os", since = "1.4.0")]
 impl IntoRawFd for fs::File {
     fn into_raw_fd(self) -> RawFd {