Destructuring binds names to parts of a value where a local binding or function parameter is declared. Associative destructuring selects values by key rather than position, making map-shaped inputs easier to use without repeated lookups. It works in `let`, `fn`, and `defn` binding forms. section 4.6 section 3.1.1 section 2.1.2
Bind map values
`(let [m {:x 1 :y 2} {x :x y :y} m] [x y])` ;; => [1 2] In `{x :x}`, the symbol `x` receives the value at key `:x`. For keyword keys that match the desired local names, `{:keys [x y]}` is shorter. The same map binding can include `:as original` to retain the entire input map. section 4.6
The map binding form provides several ways to choose what remains available in the body:
- `:keys`, `:strs`, and `:syms` bind values from keyword, string, and symbol keys, respectively. section 4.6
- `:or` supplies a default when a key is absent, not when its value is explicitly `nil`. With `{:keys [z t] :or {z 3 t 4}}` and `{:z nil}`, the bindings are `z = nil` and `t = 4`. section 4.6
- `:as` binds a name to the original collection. Binding forms can also nest: a map value may be destructured as another map or as a sequence. section 4.6
Unpack a function argument
`(defn contact-line [{:keys [name] {:keys [city]} :address}] (str name " lives in " city))` Here the function parameter binds `name` from the outer map and `city` from its nested `:address` map. Destructuring in the parameter list avoids separate lookups in the body; `let` is useful when that binding is impractical at the parameter boundary. section 4.6 section 3.1.1
Destructuring is binding syntax, not a series of assignments to an existing map. The standard-library function `destructure` exposes the transformation: it converts binding expressions into ordinary binding pairs used by macros such as `let` and `fn`. For a value threaded through differently positioned operations, `as->` can also use a destructuring form as its binding name; each subsequent value must remain compatible with that form. This `as->` capability is available from Clojure 1.8. section 4.6 section 2.3.5
