Rollup merge of #39459 - phungleson:fix-short-hand-struct-doc, r=steveklabnik

Fix short hand struct doc

Don't want to discredit @hngiang effort on this issue.

I just want to lend a hand to fix this issue #38830, it is a very nice feature and is seemingly completed.

Fixes #39096

r? @steveklabnik

src/doc/book/structs.md

@@ -117,6 +117,30 @@ fn main() {
 }
 ```
 
+Initialization of a data structure (struct, enum, union) can be simplified if
+fields of the data structure are initialized with variables which has same
+names as the fields.
+
+```
+#![feature(field_init_shorthand)]
+
+#[derive(Debug)]
+struct Person<'a> {
+    name: &'a str,
+    age: u8
+}
+
+fn main() {
+    // Create struct with field init shorthand
+    let name = "Peter";
+    let age = 27;
+    let peter = Person { name, age };
+
+    // Print debug struct
+    println!("{:?}", peter);
+}
+```
+
 # Update syntax
 
 A `struct` can include `..` to indicate that you want to use a copy of some

src/doc/reference.md

@@ -2765,6 +2765,28 @@ let base = Point3d {x: 1, y: 2, z: 3};
 Point3d {y: 0, z: 10, .. base};
 ```
 
+#### Struct field init shorthand
+
+When initializing a data structure (struct, enum, union) with named fields,
+allow writing `fieldname` as a shorthand for `fieldname: fieldname`. This
+allows a compact syntax for initialization, with less duplication.
+
+In the initializer for a `struct` with named fields, a `union` with named
+fields, or an enum variant with named fields, accept an identifier `field` as a
+shorthand for `field: field`.
+
+Example:
+
+```
+# #![feature(field_init_shorthand)]
+# struct Point3d { x: i32, y: i32, z: i32 }
+# let x = 0;
+# let y_value = 0;
+# let z = 0;
+Point3d { x: x, y: y_value, z: z };
+Point3d { x, y: y_value, z };
+```
+
 ### Block expressions
 
 A _block expression_ is similar to a module in terms of the declarations that