implement type-changing-struct-update

put the test dir in test/ui/rfcs

1 files changed, 33 insertions, 0 deletions

diff --git a/src/doc/unstable-book/src/language-features/type-changing-struct-update.md b/src/doc/unstable-book/src/language-features/type-changing-struct-update.md
new file mode 100644
index 00000000000..9909cf35b5b
--- /dev/null
+++ b/src/doc/unstable-book/src/language-features/type-changing-struct-update.md
@@ -0,0 +1,33 @@
+# `type_changing_struct_update`
+
+The tracking issue for this feature is: [#86555]
+
+[#86555]: https://github.com/rust-lang/rust/issues/86555
+
+------------------------
+
+This implements [RFC2528]. When turned on, you can create instances of the same struct
+that have different generic type or lifetime parameters.
+
+[RFC2528]: https://github.com/rust-lang/rfcs/blob/master/text/2528-type-changing-struct-update-syntax.md
+
+```rust
+#![allow(unused_variables, dead_code)]
+#![feature(type_changing_struct_update)]
+
+fn main () {
+    struct Foo<T, U> {
+        field1: T,
+        field2: U,
+    }
+
+    let base: Foo<String, i32> = Foo {
+        field1: String::from("hello"),
+        field2: 1234,
+    };
+    let updated: Foo<f64, i32> = Foo {
+        field1: 3.14,
+        ..base
+    };
+}
+```