Add impl AsFd variants of the <Fd: AsFd> examples.

Author: sunfishcode

examples/flexible-apis.rs

@@ -31,6 +31,12 @@ fn use_fd_b<Fd: AsFd>(fd: Fd) {
     let _ = fd.as_fd();
 }
 
+/// Another way to do this is to use an `impl AsFd` parameter.
+#[cfg(all(feature = "close", not(windows)))]
+fn use_fd_c(fd: impl AsFd) {
+    let _ = fd.as_fd();
+}
+
 /// The simplest way to accept a consumed I/O resource is to simply use an
 /// `OwnedFd` as an argument. Similar to `use_fd_a`, this doesn't require the
 /// function to have any type parameters, and also works in FFI signatures.
@@ -51,6 +57,12 @@ fn consume_fd_b<Fd: IntoFd>(fd: Fd) {
     let _ = fd.into_fd();
 }
 
+/// Another way to do this is to use an `impl IntoFd` parameter.
+#[cfg(all(feature = "close", not(windows)))]
+fn consume_fd_c(fd: impl IntoFd) {
+    let _ = fd.into_fd();
+}
+
 /// Now let's see how the APIs look for users.
 #[cfg(all(feature = "close", not(windows)))]
 fn main() {
@@ -59,20 +71,30 @@ fn main() {
     // The simple option requires an `.as_fd()` at the callsite.
     use_fd_a(f.as_fd());
 
-    // The other option can take a reference to any owning type directly.
+    // Another option can take a reference to any owning type directly.
     use_fd_b(&f);
 
     // Of course, users can still pass in `BorrowedFd` values if they want to.
     use_fd_b(f.as_fd());
 
+    // The other option is `impl AsFd`.
+    use_fd_c(&f);
+
+    // Users can still pass in `BorrowedFd` values if they want to here too.
+    use_fd_c(f.as_fd());
+
     let a = std::fs::File::open("Cargo.toml").unwrap();
     let b = std::fs::File::open("Cargo.toml").unwrap();
+    let c = std::fs::File::open("Cargo.toml").unwrap();
 
     // The simple option requires an `.into_fd()` at the callsite.
     consume_fd_a(a.into_fd());
 
-    // The other option can take any `IntoFd` type directly.
+    // Another option can take any `IntoFd` type directly.
     consume_fd_b(b);
+
+    // The other option can take any `IntoFd` type directly.
+    consume_fd_c(c);
 }
 
 #[cfg(windows)]