created_at2023-08-31 18:47:17.329135
updated_at2024-06-21 18:47:24.878883
descriptionSDK for writing smart contracts
Willem Wyndham (willemneal)




Build composable, upgradeable, secure Smart Contracts.

  • Composable: With Loam SDK, you compose your smart contract from many sub contracts. Subcontracts are like lego blocks that you can either use off-the-shelf from the open source ecosystem or that you can build yourself. A single Loam smart contract is composed of one or more subcontracts.

  • Upgradeable: The one subcontract that all Loam smart contracts must include (loam-subcontract-core) adds an important method to the smart contract: redeploy. You can call this method to switch the wasm hash—the behavior/brains of the contract—to a new one, while keeping the same contract ID. The storage accessed by each particular subcontract is loaded lazily, so upgrading one subcontract does not require migrating the data of another; each subcontract within your smart contract can be considered and upgraded independently.

  • Secure: The core subcontract also adds admin_set and admin_get to your contract, to make sure that only your trusted admin account can call redeploy. Our full loam architecture, beyond Loam SDK, also includes a universal factory contract, which makes it possible to deploy your contract and call admin_set in a single transaction, helping avoid front-running.

  • Subcontracts

  • Core

  • Using the Core Subcontract


A subcontract is a type that implements the IntoKey trait, which is used for lazily loading and storing the type.

Creating Subcontracts

Here's an example of how to create a subcontract:

pub struct Messages(Map<Address, String>);

This generates the following implementation:

impl IntoKey for Messages {
    type Key = IntoVal<Env, RawVal>;
    fn into_key() -> Self::Key {

External API

You can also create and implement external APIs for contract subcontracts:

pub trait IsPostable {
    fn messages_get(&self, author: Address) -> Option<String>;
    fn messages_set(&mut self, author: Address, text: String);

Core Subcontract

The Core trait provides the minimum logic needed for a contract to be redeployable. A contract should be able to be redeployed to another contract that can also be redeployed. Redeployment requires admin status, as it would be undesirable for an account to redeploy the contract without permission.

Using Core

To use the core subcontract, create a Contract struct and implement Core for it. This makes Contract redeployable by the Admin of the contract and will continue to be redeployable if the new contract also implements Core. After Core other Subcontracts can be added as needed.

use loam_sdk::{soroban_contract, soroban_sdk};
use loam_subcontract_core::{Admin, Core};

pub struct Contract;

impl Core for Contract {
    type Impl = Admin;


This code generates the following implementation:

struct SorobanContract;

impl SorobanContract {
     pub fn admin_set(env: Env, admin: Address) {
    pub fn admin_get(env: Env) -> Option<Address> {
    pub fn redeploy(env: Env, wasm_hash: BytesN<32>) {
    // Subcontract methods would be inserted here.
    // Contract must implement all Subcontracts and is the proxy for the contract calls.
    // This is because the Subcontracts have default implementations which call the associated type

By specifying the associated Impl type for Core, you enable the default Admin methods to be used (admin_set, admin_get, redeploy). However, you can also provide a different implementation if needed by replacing Admin with a different struct/enum that also implements IsCore.

Notice that the generated code calls Contract::redeploy and other methods. This ensures that the Contract type is redeployable, while also allowing for extensions, as Contract can overwrite the default methods.

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cargo fmt