Clarity reference - Part 2 / Data-Space Primitives

Data within a smart contract’s data-space is stored within maps.

maps associate a pair of two values (a, b) (also known as a tuple) to another tuple. It works similarly to a name-value pair.

To get or set a value in a map you use:

(map-get map-name key-tuple) – This fetches the value associated with a given key in the map, or returns none if there is no such value.
(map-set! map-name key-tuple value-tuple) – This will set the value of key-tuple in the data map.
(map-insert! map-name key-tuple value-tuple) – This will set the value of key-tuple in the data map if and only if an entry does not already exist.
(map-delete! map-name key-tuple) – This will delete key-tuple from the data map.

A smart contract defines the data schema of a data map through define-map.

Primitive Types

Clarity is a strongly-typed language. Its type system has the following types:

(tuple (key-name-0 key-type-0) (key-name-1 key-type-1) ...) – a typed tuple with named fields.
(list max-len entry-type) – a list of maximum length max-len, with entries of type entry-type.
(response ok-type err-type) – used by public functions to commit their changes or abort.
(optional some-type) – an option type for objects that can either be (some value) or none.
principal – object representing a principal. A principal represents the address on the blockchain. There are two types of principals: standard principal (has private key) and contract principal (points to a smart contract).
bool – boolean value (true or false)
int – signed 128-bit integer
uint – unsigned 128-bit integer
“unknown types” – the type system does not generally allow them