Rollup merge of #52003 - Kerollmops:option-replace, r=Kimundi

Implement `Option::replace` in the core library

Here is the implementation of the `Option::replace` method. The first step of [the tracking issue #51998](https://github.com/rust-lang/rust/issues/51998).

2 files changed, 16 insertions, 0 deletions

diff --git a/src/libcore/tests/lib.rs b/src/libcore/tests/lib.rs
index 9d4a5213992..ca7db6e4639 100644
--- a/src/libcore/tests/lib.rs
+++ b/src/libcore/tests/lib.rs
@@ -44,6 +44,7 @@
 #![feature(reverse_bits)]
 #![feature(iterator_find_map)]
 #![feature(slice_internals)]
+#![feature(option_replace)]
 
 extern crate core;
 extern crate test;
diff --git a/src/libcore/tests/option.rs b/src/libcore/tests/option.rs
index 22109e28edd..bc3e61a4f54 100644
--- a/src/libcore/tests/option.rs
+++ b/src/libcore/tests/option.rs
@@ -297,3 +297,18 @@ fn test_try() {
     }
     assert_eq!(try_option_err(), Err(NoneError));
 }
+
+#[test]
+fn test_replace() {
+    let mut x = Some(2);
+    let old = x.replace(5);
+
+    assert_eq!(x, Some(5));
+    assert_eq!(old, Some(2));
+
+    let mut x = None;
+    let old = x.replace(3);
+
+    assert_eq!(x, Some(3));
+    assert_eq!(old, None);
+}