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1. The Motoko Programming Language
2.
3. Part 1
4. 1. Introduction
❱
5. 1. 1.1. Getting Started
6. 2. Common Programming Concepts
❱
7. 1. 2.1. Variables
2. 2.2. Mutability
3. 2.3. Comments
4. 2.4. Types
❱
5. 1. 2.4.1. Tuples
2. 2.4.2. Records
3. 2.4.3. Variants
4. 2.4.4. Immutable Arrays
5. 2.4.5. Mutable Arrays
6. 2.5. Operators
❱
7. 1. 2.5.1. Numeric operators
2. 2.5.2. Relational operators
3. 2.5.3. Assignment operators
4. 2.5.4. Text concatenation
5. 2.5.5. Logical expressions
6. 2.5.6. Bitwise operators
7. 2.5.7. Operator precedence
8. 2.6. Pattern Matching
9. 2.7. Functions
10. 2.8. Options and Results
11. 2.9. Control Flow
❱
12. 1. 2.9.1. If Expression
2. 2.9.2. If Else Expression
3. 2.9.3. Switch Expression
13. 2.10. Objects and Classes
❱
14. 1. 2.10.1. Objects
2. 2.10.2. Classes
15. 2.11. Modules and Imports
16. 2.12. Assertions
8. 3. Internet Computer Programming Concepts
❱
9. 1. 3.1. Actors
❱
2. 1. 3.1.1. From Actor to Canister
2. 3.1.2. Canister Calls from Clients
3. 3.2. Principals and Authentication
4. 3.3. Async Data
❱
5. 1. 3.3.1. Shared Types
2. 3.3.2. Candid
6. 3.4. Basic Memory Persistence
❱
7. 1. 3.4.1. Upgrades
2. 3.4.2. Stable Variables
10.
11. Part 2
12. 4. Advanced Types
❱
13. 1. 4.1. Generic Types
2. 4.2. Subtyping
3. 4.3. Recursive Types
4. 4.4. Type Bounds
14. 5. The Base Library
❱
15. 1. 5.1. Primitive Types
❱
2. 1. 5.1.1. Bool
2. 5.1.2. Nat
3. 5.1.3. Int
4. 5.1.4. Float
5. 5.1.5. Principal
6. 5.1.6. Text
7. 5.1.7. Char
8. 5.1.8. Bounded Number Types
❱
9. 1. 5.1.8.1. Nat8
2. 5.1.8.2. Nat16
3. 5.1.8.3. Nat32
4. 5.1.8.4. Nat64
5. 5.1.8.5. Int8
6. 5.1.8.6. Int16
7. 5.1.8.7. Int32
8. 5.1.8.8. Int64
10. 5.1.9. Blob
3. 5.2. Utility Modules
❱
4. 1. 5.2.1. Iterators
2. 5.2.2. Hash
3. 5.2.3. Option
4. 5.2.4. Result
5. 5.2.5. Order
6. 5.2.6. Error
7. 5.2.7. Debug
5. 5.3. Data Structures
❱
6. 1. 5.3.1. Array
2. 5.3.2. List
3. 5.3.3. Buffer
4. 5.3.4. HashMap
5. 5.3.5. RBTree
7. 5.4. More Data Structures
8. 5.5. IC APIs
❱
9. 1. 5.5.1. Time
2. 5.5.2. Timer
3. 5.5.3. CertifiedData
4. 5.5.4. Random
5. 5.5.5. Experimental
16. 6. Advanced Concepts
❱
17. 1. 6.1. Async Programming
2. 6.2. Scalability
❱
3. 1. 6.2.1. Actor Classes
2. 6.2.2. Stable Storage
4. 6.3. System API's
❱
5. 1. 6.3.1. Message Inspection
2. 6.3.2. Timers
3. 6.3.3. Certified Variables
4. 6.3.4. Pre-upgrade and Post-upgrade
5. 6.3.5. Cryptographic Randomness
18.
19. Part 3
20. 7. Project Deployment
❱
21. 1. 7.1. Installing the SDK
2. 7.2. Local Deployment
3. 7.3. Canister Status
4. 7.4. Identities and PEM Files
5. 7.5. Cycles and ICP
6. 7.6. Cycles Wallet
7. 7.7. IC Deployment
22. 8. Common Internet Computer Canisters
❱
23. 1. 8.1. IC Management Canister
2. 8.2. ICP Ledger Canister
3. 8.3. Cycle Minting Canister
24. 9. Internet Computer Standards
❱
25. 1. 9.1. ICRC1
26. 10. Tokenized Comments Example
27.
28. APPENDIX
29. 11. TABLES
* Light
* Rust
* Coal
* Navy
* Ayu
THE MOTOKO PROGRAMMING LANGUAGE BOOK
SHARED TYPES
Incoming and outgoing data are defined by the argument types and return types of
public shared functions inside actors. Incoming and outgoing data types are
restricted to a subset of available Motoko types, called shared types.
Shared types are always immutable types or data structures composed of immutable
types (like records, objects and variants).
Shared types get their name from being sharable with the outside world, that is
the wider internet beyond the actors running in canisters on the Internet
Computer.
SHARED TYPES IN PUBLIC SHARED FUNCTIONS
Only shared types are allowed for arguments and return values of public shared
functions. We give examples of a custom public shared function type called
SharedFunction to illustrate shared types. Recall that a public shared function
type includes the shared and async keywords.
Here are the most important shared types in Motoko.
SHARED PRIMITIVE TYPES
All primitive types (except the Error type) are shared.
type SharedFunction = shared Nat -> async Text;
The argument of type Nat and the return value of type Text are shared types.
SHARED OPTION TYPES
Any shared type in Motoko can be turned into an Option type which remains
shared.
type SharedFunction = shared ?Principal -> async ?Bool;
The argument of type ?Principal and the return value of type ?Bool are shared
types.
SHARED TUPLE TYPES
Tuples consisting of shared types are also shared, that is they are shared tuple
types.
type SharedFunction = shared (Nat, Int, Float) -> async (Principal, Text);
The argument (Nat, Int, Float) and the return value (Principal, Text) are shared
tuple types.
SHARED IMMUTABLE ARRAY TYPES
Immutable arrays consisting of shared types are also shared, that is they are
shared immutable array types.
type SharedFunction = shared [Int] -> async [Nat];
The types [Int] and [Nat] are shared immutable array types.
SHARED VARIANT TYPES
Variant types that have shared associated types are also shared.
type GenderAge = {
#Male : Nat;
#Female : Nat;
};
type SharedFunction = shared GenderAge -> async GenderAge;
The variant type GenderAge is a shared type because Nat is also shared.
SHARED OBJECT TYPES
Object types that have shared field types are also shared.
type User = {
id : Principal;
genderAge : GenderAge;
};
type SharedFunction = shared User -> async User;
Object type User is a shared type because Principal and GenderAge are also
shared types.
SHARED FUNCTION TYPES
Shared function types are also shared types. This example shows a shared public
function that has another shared public function as its argument and return
type.
type CheckBalance = shared () -> async Nat;
type SharedFunction = shared CheckBalance -> async CheckBalance;
CheckBalance is a shared type because it is the type of a public shared
function.
SHARED ACTOR TYPES
All actor types are shared types.
type Account = actor {
checkBalance : shared () -> async Nat;
};
type SharedFunction = shared Account -> async Account;
Account is a shared type because it is the type of an actor.