Lesson 12 Doubts

[adityabhattad2021]

ref: https://github.com/PatrickAlphaC/hardhat-erc20-fcc/blob/main/contracts/ManualToken.sol

1. Can someone please explain working of

mapping(address => mapping(address => uint256)) public allowance;

2. What does this mapping exactly do (an example will be very helpful) ?
3. Please explain

uint8 public decimals = 18;
totalSupply = initialSupply * 10**uint256(decimals);

Lets see we put initialSupply = 100, what will be the total supply?
4. Will this tokens be in terms of Wei like 1 ETH= 1000000000000000000 Wei ?
5. A brief intro to stable coins would be helpful ( Can this tokens be stable coin ? )
6. Why this line

// Check for overflows
require(balanceOf[_to] + _value >= balanceOf[_to]);

as the above require statement will be logically be always true, then why check, is there any way balanceOf[_to] + _value >= balanceOf[_to]) can be false?

[aman-webdev]

1. The mapping is from tokenholder->address of smart contract allowed to use those tokens -> how much of tokens were allowed.
2. We need to track which address has allowed another address how many tokens, the mapping does that only
3. Yes, 18 decimals mean the token can be divided upto 18 decimal points and since solidity doesn't support float, we multiply with 10^18
4. Yes

[adityabhattad2021]

Lets say we put initialSupply = 100, what will be the total supply?
And total supply in terms of
1 MYTOKEN= ? ETH
1 MYTOKEN= ? Wei
Thanks of taking out your precious time.

[aman-webdev]

since initial supply is 100 it would mean there are a total of 100* 10^18 = 10^20 Tokens, So 1 Token would mean 10^18 wei. The decimals just means upto how many decimal places can the token divided into

[krakxn]

1 and 2:

DSA will help in such cases.

mapping(address => mapping(address => uint256)) public allowance; basically maps the address key to the mapping(address => uint256) mapping.

Going deeper, that mapping(address => uint256) itself has a key which points to a uint256 type -- which here is our allowance.

3 and 4:

uint8 public decimals = 18;
totalSupply = initialSupply * 10**uint256(decimals);

Refer here for the above: https://github.com/ethereumjs/ethereumjs-units/blob/master/units.json

After going through it you can answer it yourself. If not, of course, reply and I will help. But try by yourself first.

5:

Stablecoins are cryptocurrencies backed 1:1 to their native currency, for example: $USDT is pegged to the US Dollar.

6:

This is an old way to do it (refer SafeMath), as we do not really have to check for overflows in the newer Solidity, it is now done automatically by the compiler. So, omitting wouldn't be harmful here.

[adityabhattad2021]

So,
Here if we put initialSupply=100 :

uint8 public decimals = 18;
totalSupply = initialSupply * 10**uint256(decimals);

I can assume total supply to be 100 MYTOKENS
where 1 MYTOKEN = 10^18 Wei
and 1 MYTOKEN = 1 ETH

[krakxn]

That is correct, as is denominated the same way as ETH.

However, this -- and 1 MYTOKEN = 1 ETH -- is partially wrong.

In a real world scenario, the above will not be pegged 1:1 to ETH , unless it is one of the prerequisites of the cryptocurrency. There are many factors involved, and to add to that is this being a volatile and risk-on market.

[adityabhattad2021]

Thanks for being so helpful @krakxn .

[krakxn]

No problem, all the best!

Further note: Whilst arbitrageurs are usually active for depegs, if someone really wanted they could easily manipulate an illiquid altcoin.