Macro field 

macro_rules! field {
    ($s:ident . $f:ident) => { ... };
    (& $s:ident . $f:ident) => { ... };
    (&mut $s:ident . $f:ident) => { ... };
}

Access a field of an anonymous struct object.

use structz::*;

let mut person = stru! {
    name: "John Doe",
    age: 26,
    tags: vec!["developer", "rustacean"],
};

// immutable borrow
assert_eq!(field!(&person.name), &"John Doe");

// mutable borrow
*field!(&mut person.age) += 1;
assert_eq!(field!(&person.age), &27);

// consume the struct and get the field value
let tags = field!(person.tags);
assert_eq!(tags, vec!["developer", "rustacean"]);

// `person` cannot be used anymore.

Unlike the built-in member access operator ., structz uses some type deduction magic to achieve access to the specified field. Therefore, it is not smart enough: it cannot move a value of certain field out while keeping other fields remain valid, and it also cannot avoid consume the entire struct object while moving a value that implements Copy out.

However, if all fields implement Copy, then the anonymous struct will also implement Copy:

use structz::*;

let pos = stru! {
    x: 300,
    y: 480,
    marker: "Block",
};
assert_eq!(field!(pos.x), 300);
assert_eq!(field!(pos.y), 480);
assert_eq!(field!(pos.marker), "Block");