Accessing and Updating Objects

The reader has seen these patterns across four earlier chapters. This section brings them together.

Static Access: Colon Syntax (Ch 12)

user:name                  ;; → user.name
user:address:city          ;; → user.address.city

Dynamic Access: `get` (Ch 12)

(get user key)             ;; → user[key]
(get user :name)           ;; → user["name"]

Immutable Updates: `assoc` / `dissoc` (Ch 13)

(bind updated (assoc user :age 43 :active true))
(bind trimmed (dissoc user :temp-id))

const updated = {...user, age: 43, active: true};
const trimmed = (() => {
  const {tempId: ___gensym0, ...rest__gensym1} = user;
  return rest__gensym1;
})();

assoc uses spread — the original is unchanged. dissoc uses destructuring to extract and discard the key, returning the rest.

Structural Matching (Ch 10)

(match response
  ((obj :ok true :data d) (process d))
  ((obj :ok false :error e) (handle-error e))
  (_ (throw (new Error "unexpected response"))))

Four features, four chapters, one data structure. Construction with obj, access with colons and get, updates with assoc/dissoc, pattern matching with structural match. The reader who has followed the book to this point already knows how to work with objects — this chapter adds the deeper mechanics.

Lykn