Creating Smart Contracts

A smart contract is an immutable program consisting of a set of logic (state variables, functions, event handlers, etc.) or rules that can be deployed, stored, and accessed on a distributed ledger technology such as Hedera. The functions contained within a smart contract can update and manage the state of the contract and read data from the deployed contract. They may also create and call other smart contracts functions on the network. Smart contracts are secure, tamper-proof, and transparent, offering a new level of trust and efficiency.

Hedera supports any language that compiles to the Ethereum Mainnet. This includes Solidity and Vyper. These programming languages compile code and produce bytecode that the Ethereum Virtual Machine (EVM) can interpret and understand.

• To learn more about the Solidity programming language, check out the documentation maintained by the Solidity team here.

• To learn more about Vyper, check out the documentation maintained by the Vyper team here.

In addition, many tools are available to write and compile smart contracts, including the popular Remix IDE and Hardhat. The Remix IDE is a user-friendly platform that allows you to easily write and compile your smart contracts and perform other tasks such as debugging and testing. Using these tools, you can create powerful and secure smart contracts that can be used for various purposes, from simple token transfers to complex financial instruments.

Example

The following is a very simple example of a smart contract written in the Solidity programming language. The smart contract defines the owner and message state variables, along with functions like set_message (which modifies state details by writing) and get_message(which reads state details).

pragma solidity >=0.7.0 <0.8.9;

contract HelloHedera {
    // the contract's owner, set in the constructor
    address owner;

    // the message we're storing
    string message;

    constructor(string memory message_) {
        // set the owner of the contract for `kill()`
        owner = msg.sender;
        message = message_;
    }

    function set_message(string memory message_) public {
        // only allow the owner to update the message
        require(msg.sender == owner);
        message = message_;
    }

    // return a string
    function get_message() public view returns (string memory) {
        return message;
    }
}

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Things you should consider when creating a contract

Automatic Token Associations

An auto association slot is one or more slots you approve that allow tokens to be sent to your contract without explicit authorization for each token type. If this property is not set, you must associate each token before it is transferred to the contract for the transfer to be successful via the TokenAssociateTransaction in the SDKs. Learn more about auto-token associations here.

This functionality is exclusively accessible when configuring a ContractCreateTransaction API through the Hedera SDKs. If you are deploying a contract on Hedera using EVM tools such as Hardhat and the Hedera JSON RPC Relay, please note that this property cannot be configured, as EVM tools lack compatibility with Hedera's unique features.

Admin Key

Contracts have the option to have an admin key. This concept is native to Hedera contracts and allows the contract account properties to be updated. Note that this does not impact the contract bytecode and does not relate to upgradability. If the admin key is not set, you will not be able to update the following Hedera native properties (noted in ContractUpdateTransactionBody protobuf) for your contract once it is deployed:

• autoRenewPeriod
• memoField
• max_automatic_token_associations
• auto_renew_account_id
• staked_id
• decline_reward

You cannot set the admin key field if you deploy a contract via tools like Hardhat. This field can be set if desired by deploying a contract using one of the Hedera SDKs.

Max Contract Storage Size

Each contract on Hedera has a storage size limit of 16,384,000 key value pairs (~500MB).

Rent

While rent is not enabled for contracts deployed on Hedera today, you will want to be familiar with the concept of rent, as it may potentially impact the costs of maintaining your contract state on the network. Please refer to the Smart Contract Rent documentation here.

Transaction and Gas Fees

There are Hedera transaction fees and EVM fees associated with deploying a contract. To view the list of base fees, check out the fees page here and the fee estimator calculator here.

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Smart Contract FAQs

What is a smart contract?

A smart contract is a program that is written in a language that can be interpreted by the EVM. Please refer to the glossary for more keywords and definitions.

What programming language does Hedera support for smart contracts?

Hedera supports the official Ethereum Virtual Machine and therefore any smart contract language that conforms to standard EVM code, such as Solidity or Vyper.

Can I write and compile my smart contracts using Remix IDE or other Ethereum ecosystem tools?

You can use Remix IDE or other Ethereum ecosystem tools to write, compile, and deploy your smart contract on Hedera. Check out our EVM-compatible tools here.

Where can I find the smart contracts that are deployed to each Hedera network (previewnet, testnet, mainnet)?

On your favorite trusted Block Explorer (also called Mirror Node Explorer on Hedera). To view community-hosted explorers check out the network explorer tools page here.

Which ERC token standards are supported on Hedera?

Hedera supports ERC-20 and ERC-721 token standards and can find the full list of supported standards here.