added docs and example function

Author: mj10021

library/core/src/lib.rs

@@ -271,10 +271,11 @@
 #[allow(unused_extern_crates)]
 extern crate self as core;
 
+#[allow(unused_imports)]
+use crate::marker::FnPtr;
 #[prelude_import]
 #[allow(unused)]
 use prelude::v1::*;
-
 #[cfg(not(test))] // See #65860
 #[macro_use]
 mod macros;
@@ -440,5 +441,4 @@ pub mod simd {
     #[unstable(feature = "portable_simd", issue = "86656")]
     pub use crate::core_simd::simd::*;
 }
-
 include!("primitive_docs.rs");

library/core/src/primitive_docs.rs

@@ -1552,6 +1552,7 @@ mod prim_ref {}
 /// * [`Clone`]
 /// * [`Copy`]
 /// * [`Send`]
+/// * [`Sized`]
 /// * [`Sync`]
 /// * [`Unpin`]
 /// * [`UnwindSafe`]
@@ -1591,3 +1592,18 @@ impl<Ret, T> Clone for fn(T) -> Ret {
 impl<Ret, T> Copy for fn(T) -> Ret {
     // empty
 }
+
+// Fake impl that's only really used for docs.
+#[cfg(doc)]
+#[unstable(
+    feature = "fn_ptr_trait",
+    issue = "none",
+    reason = "internal trait for implementing various traits for all function pointers"
+)]
+#[doc(fake_variadic)]
+/// This trait is implemented on function pointers with any number of arguments.
+impl<Ret, T> FnPtr for fn(T) -> Ret {
+    fn addr(self) -> *const () {
+        // empty
+    }
+}

library/std/src/lib.rs

@@ -347,6 +347,7 @@
 #![feature(core_panic)]
 #![feature(custom_test_frameworks)]
 #![feature(edition_panic)]
+#![feature(fn_ptr_trait)]
 #![feature(format_args_nl)]
 #![feature(get_many_mut)]
 #![feature(lazy_cell)]
@@ -376,10 +377,11 @@
 
 // Explicitly import the prelude. The compiler uses this same unstable attribute
 // to import the prelude implicitly when building crates that depend on std.
+#[allow(unused_imports)]
+use crate::marker::FnPtr;
 #[prelude_import]
 #[allow(unused)]
 use prelude::rust_2021::*;
-
 // Access to Bencher, etc.
 #[cfg(test)]
 extern crate test;

library/std/src/primitive_docs.rs

@@ -1552,6 +1552,7 @@ mod prim_ref {}
 /// * [`Clone`]
 /// * [`Copy`]
 /// * [`Send`]
+/// * [`Sized`]
 /// * [`Sync`]
 /// * [`Unpin`]
 /// * [`UnwindSafe`]
@@ -1591,3 +1592,18 @@ impl<Ret, T> Clone for fn(T) -> Ret {
 impl<Ret, T> Copy for fn(T) -> Ret {
     // empty
 }
+
+// Fake impl that's only really used for docs.
+#[cfg(doc)]
+#[unstable(
+    feature = "fn_ptr_trait",
+    issue = "none",
+    reason = "internal trait for implementing various traits for all function pointers"
+)]
+#[doc(fake_variadic)]
+/// This trait is implemented on function pointers with any number of arguments.
+impl<Ret, T> FnPtr for fn(T) -> Ret {
+    fn addr(self) -> *const () {
+        // empty
+    }
+}