Types and Interface

Smart contracts expose functions so users can interact with them. There are different types of functions including read-only, private and payable.

SDK types

Smart contracts can receive, store, and return data using native Rust types such as strings, integers, booleans, maps, and vectors. The SDK also provides types for values that need special handling at the contract boundary.

Large integers

Contracts can store u64 and u128 values directly, but JSON consumers cannot always represent them without losing precision. Use the SDK’s U64 and U128 wrapper types for public inputs and outputs that need to be serialized as strings.

JavaScript numbers cannot represent every integer above 2^53 - 1. Keep native integer types in internal contract logic, and use the JSON wrapper types at the external interface when necessary.

Complex objects

Contracts can receive and return complex Rust structures. Objects used as JSON inputs or outputs need JSON serialization, while structures stored in contract state need Borsh serialization.

#[near(serializers = [json])]
pub struct Bid {
    pub bidder: AccountId,
    pub amount: U128,
}

See serialization for the difference between interface and state serialization.

Tokens and accounts

Use NearToken to represent NEAR amounts. It provides constructors and accessors for yoctoNEAR, millinear, and NEAR values.

let deposit = NearToken::from_near(1);
let amount = deposit.as_yoctonear();

The SDK’s AccountId type validates NEAR account IDs when values enter the contract. Prefer it to a plain String whenever a value represents an account.

Building Smart Contracts

DevKit

Tutorials

Types and Interface

SDK types

Large integers

Complex objects

Tokens and accounts

​SDK types

​Large integers

​Complex objects

​Tokens and accounts

SDK types

Large integers

Complex objects

Tokens and accounts