Thread by @LearnWithSiv

SOLIDITY BASICS - 7 (Loops, Constructors, Modifiers & Sending ETH) 🛸🪐

Digest 12 of "Learn Blockchain, Solidity, and Full Stack Web3 Development with JavaScript – 32-Hour Course" by @PatrickAlphaC ⭐🤩

A Thread.🧵

#solidity #coding #blockchain #smartcontracts #web3 🚀

@PatrickAlphaC Check out the previous thread of the series here 👇🏽

https://twitter.com/LearnWithSiv/status/1534199324803928065

@PatrickAlphaC 📚In this lesson we see how to withdraw the deposited funds from our contract. 🤑
We cover:
- for loop
- ways to transfer eth
- constructors
- modifiers

@PatrickAlphaC BASIC SOLIDITY LOOP 📍
- for loop syntax:

✅for (startingIndex; endingIndex; stepAmount);

@PatrickAlphaC - Within the withdraw() function, add a for loop statement

✅for(uint256 funderIndex=0; funderIndex < funders.length; funderIndex++);

-> funders.length = length of the funders array

@PatrickAlphaC ✔️ Upon calling the withdraw() function, the funds have to be transferred and the funders array has to be reset.

@PatrickAlphaC ✅
address funder = funders[funderIndex];
addressToAmount[funder]=0;
funders=new address[](0); // implies that it has 0 objects

@PatrickAlphaC SENDING ETH 💰
1. transfer
2. send
3. call

@PatrickAlphaC USING transfer() 💸

✅payable(msg.sender).transfer(address(this).balance); // "this" here refers to this contract

💡msg.sender is type cast to payable type which is otherwise of address type.

@PatrickAlphaC USING send() 💸

✅bool ret=payable(msg.sender).send(address(this).balance);

- The send() returns a boolean if the transfer is successful. However, if send() fails, we need to revert the state. ⚠️

✅require(ret,"send failed");

@PatrickAlphaC USING call() 🤑

✅(bool ret,)=payable(msg.sender).call{value:address(this).balance}("");

- the call() function returns more than 1 variable but we're only interested in knowing if the call went through or not.
- Revert the state if call fails ⚠️

✅require(ret,"call failed");

@PatrickAlphaC 🚨Note:
✔️call() is the recommended transfer method.
✔️Check out solidity-by-example.org/sending-ether/ for more.

@PatrickAlphaC BASIC SOLIDITY CONSTRUCTOR 💻
- A constructor is a function that gets immediately called in the same transaction that we create the contract.
- use the "constructor" keyword. ✔️

@PatrickAlphaC 🚨Note:
Only the owner must be able to withdraw the funds.
See how to ensure that below 👇🏽

@PatrickAlphaC ✅address public owner;

constructor(){
owner=msg.sender;
}

- This sets the owner to the user who is initiating the transaction.

@PatrickAlphaC - To ensure that only the owner initiates the withdrawal, add the statement below within the withdraw() function:

✅require(msg.sender==owner,"not owner");

OR

💡 Use a modifier :)

@PatrickAlphaC ✅modifier onlyOwner{
require(msg.sender==owner,"not owner");
_;
}

💡 The underscore _ after the first statement within the modifier implies that the rest of the code of the function is executed after the first statement of the modifier only.

@PatrickAlphaC Now, modify the withdraw function as shown 👇🏽

✅function withdraw() public onlyOwner{
....
}

@PatrickAlphaC Now, you can go ahead and try to fund/ withdraw on the testnet 🎉

@PatrickAlphaC That was 30 mins🕢 of the course summarized for you. 🙃

@PatrickAlphaC If you're a web3 enthusiast, wanting to explore, learn and grow as a developer, do watch this video and learn along with me. ✨

@PatrickAlphaC Digest 13 (summarizing the next few minutes of the course) coming soon... 😉

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