Lesson-12 IERC20 token Error

[TimeKeyRoll]

Wondering what is ALLOWANCE function is all about in ERC20?

[othaime-en]

Hey @MasterofBlockchain you are getting the error because the variables highlighted above (sender and receipent) haven't been initialized and yet you are using them. From the code in your repo, I figured you were supposed to use from and to instead. Consider making that change.

[TimeKeyRoll]

mapping(address => mapping(address => uint256)) public override allowance;
and there is allowance function in which msg.sender is choosing an address and approving it some amount for to use. @othaime-en
How does this function works? why do msg.sender has to use this function?

[othaime-en]

First, it is not a function, it is a mapping. Second, as the name suggests, it is used by the msg.sender to "allow" or give permission to another account to spend some amount of ETH that we specify. To gain more insight, you could look at how it is used. We can see that it is used inside the approve function where msg.sender approves some other account to spend some amount of their token.

[TimeKeyRoll]

Whops! lol @othaime-en ser Appreciate the explanation. I have posted my kinda explanation with it which i have understood. It is great to see that i could read this how it was written.
But question remains right there.
Why would a msg.sender would want to approve some amount for spender. What is the benefit? I know what is happening but i don't know why it is happening. lol Hope this time I am able to frame my question right.haha

[othaime-en]

Hmm...okay. If you are keen enough, you have noticed that most of the time we try and do things programmatically and not physically (for lack of a better word :) ) . A good example was the verify functionality. We didn't want to go directly to etherscan to verify so we created a simple script to do it programmatically for us right? In most cases, in this space you will be doing something of the sort. So with ERC20 tokens, there is alot of ownership changes between tokens where people buy, sell, or transfer their tokens/ETH to other accounts. Most of the time this ownership change is done programatically by some other contracts. So it is a contract transfering tokens maybe after some condition is met. This is fine and all but obviously we need a way to control this transfer because what if we don't want to send the money or what if a malicious actors tries to send themselves tokens from our account? We need a way to grant permission to other people or smart contracts to use our funds. That's why we need the allowance and approve functionality. This is useful because we get to approve/allow who our money/tokens gets sent to. So we are basically saying that hey me as msg.sender has allowed this address to use this much tokens from our balance (This mostly applies to approving smart-contracts or protocols to use our funds). You'll get to see this in action in lesson 13 hopefully. I hope this explanation is sufficient :)

[TimeKeyRoll]

that's your cool way to explain @othaime-en
I got that stored in my head.Appreciated my man. Thankyou :)

[TimeKeyRoll]

mapping(address => mapping(address => uint256)) public override allowance;
And there is allowance function in which msg.sender is choosing an address and approving it some amount for to use.
How does this function works? why do msg.sender has to use this function?

@krakxn

[othaime-en]

Hey @MasterofBlockchain please don't delete the previous post, just add the new edited post on top. The previous question may help other people.

[TimeKeyRoll]

Oh! okay. it's because question was not answered so i tried to change the question.anyway i will keep that in mind. thankyou ser.