[WIP] Document field init shorthand

src/doc/book/structs.md

@@ -117,6 +117,28 @@ fn main() {
 }
 ```
 
+We can initializing a data structure (struct, enum, union) with named fields, by writing `fieldname` as a shorthand for `fieldname: fieldname`. This allows a compact syntax for initialization, with less duplication:
+
+```
+#![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/grammar.md

@@ -510,8 +510,9 @@ unit_expr : "()" ;
 ### Structure expressions
 
 ```antlr
-struct_expr : expr_path '{' ident ':' expr
-                      [ ',' ident ':' expr ] *
+field_init : ident | ident ':' expr;
+struct_expr : expr_path '{' field_init
+                      [ ',' field_init ] *
                       [ ".." expr ] '}' |
               expr_path '(' expr
                       [ ',' expr ] * ')' |

src/doc/reference.md

@@ -2757,6 +2757,19 @@ 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:
+
+```
+let a = SomeStruct { field1, field2: expression, field3 };
+let b = SomeStruct { field1: field1, field2: expression, field3: field3 };
+```
+
 ### Block expressions
 
 A _block expression_ is similar to a module in terms of the declarations that