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Write Solidity Contracts

The dApp template ships with a starter ERC-20 contract (MyToken.sol). This guide walks through how it's structured, how to modify it, and how to add new contracts to the project. If you've completed the VS Code setup, you'll have full editor support as you work.

The Starter Contract: MyToken​

Open contracts/src/MyToken.sol:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";

contract MyToken is ERC20 {
    constructor(
        string memory name_,
        string memory symbol_,
        uint256 initialSupply
    ) ERC20(name_, symbol_) {
        _mint(msg.sender, initialSupply);
    }

    function mint(address to, uint256 amount) external {
        _mint(to, amount);
    }
}

This is a standard ERC-20 token that:

  • Accepts a name, symbol, and initial supply at deployment
  • Mints the initial supply to the deployer
  • Exposes a public mint function (no access control — suitable for development)

The contract inherits from OpenZeppelin's ERC20, which provides the full ERC-20 interface: transfer, approve, transferFrom, balanceOf, allowance, and all the standard events.

Add OpenZeppelin Dependencies​

The template includes OpenZeppelin via Foundry's dependency management. If you need to reinstall or add new OpenZeppelin libraries:

cd contracts
forge install openzeppelin/openzeppelin-contracts

Dependencies are stored in lib/ and mapped via remappings.txt:

@openzeppelin/contracts/=lib/openzeppelin-contracts/contracts/

This lets you use clean import paths like import "@openzeppelin/contracts/token/ERC20/ERC20.sol";.

Add a New Contract​

To add a new contract to the project, create a new .sol file in contracts/src/. For example, an ERC-721 NFT:

// contracts/src/MyNFT.sol
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

import "@openzeppelin/contracts/token/ERC721/ERC721.sol";

contract MyNFT is ERC721 {
    uint256 private _nextTokenId;

    constructor(string memory name_, string memory symbol_) ERC721(name_, symbol_) {}

    function mint(address to) external returns (uint256) {
        uint256 tokenId = _nextTokenId++;
        _mint(to, tokenId);
        return tokenId;
    }
}

Compile​

Build all contracts with Forge:

cd contracts
forge build

This compiles every .sol file in src/ and writes artifacts to out/. Each contract gets a JSON file containing its ABI, bytecode, deployed bytecode, and source maps. For example, out/MyToken.sol/MyToken.json contains everything needed for deployment and interaction.

After adding a new contract, you'll want to generate C# typed services so you can interact with it from .NET.

The foundry.toml Configuration​

The template's foundry.toml is minimal — Foundry's defaults work well:

[profile.default]
src = "src"
out = "out"
libs = ["lib"]

Common additions:

  • optimizer = true and optimizer_runs = 200 — enable the Solidity optimizer for production
  • via_ir = true — use the IR-based code generator (produces smaller bytecode for complex contracts)
  • solc_version = "0.8.24" — pin a specific compiler version

Next Steps​

Now that you have contracts compiling: