building-the-smart-contract.md

description
From your VSCode, checkout Lock.sol smart contract

➡️ Building the Smart Contract

Code Explanation

This page explains the default contract provided in the Hardhat boilerplate. This simple contract, named Lock, allows an owner to lock up some Ether until a specified unlock time, after which the owner can withdraw the funds.

Head over to your VSCode, open the contracts folder and checkout Lock.sol:

{% embed url="https://gist.github.com/KBPsystem777/a978883afdc0cc0230710ad47760d0a5" %} Lock.sol {% endembed %}

Detailed Breakdown

SPDX License Identifier

{% code overflow="wrap" fullWidth="true" %}

// SPDX-License-Identifier: UNLICENSED

{% endcode %}

• Indicates that the contract is unlicensed. It is important for open-source projects to include a license identifier.

Pragma Directive

{% code overflow="wrap" %}

pragma solidity ^0.8.24;

{% endcode %}

• Specifies the version of Solidity compiler to use.

Contract Definition

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contract Lock {
    uint public unlockTime;
    address payable public owner;

    event Withdrawal(uint amount, uint when);

{% endcode %}

• Defines a contract named Lock.
• Declares state variables unlockTime and owner.
• Declares an event Withdrawal that logs withdrawals.

Constructor

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constructor(uint _unlockTime) payable {
    require(
        block.timestamp < _unlockTime,
        "Unlock time should be in the future"
    );

    unlockTime = _unlockTime;
    owner = payable(msg.sender);
}

{% endcode %}

• The constructor is executed once during deployment.
• It takes an unlockTime parameter and ensures it is in the future.
• Sets the unlockTime and the owner of the contract to the deployer.

Withdraw Function

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function withdraw() public {

    require(block.timestamp >= unlockTime, "You can't withdraw yet");
    require(msg.sender == owner, "You aren't the owner");

    emit Withdrawal(address(this).balance, block.timestamp);

    owner.transfer(address(this).balance);
}

{% endcode %}

• Allows the owner to withdraw funds after the unlockTime.
• Requires the current time to be at least the unlockTime.
• Ensures that only the owner can withdraw the funds.
• Emits a Withdrawal event and transfers the contract's balance to the owner.