How to peg a token to another token

Question

I want to create a token that represent the other token, the peg is not 1:1 but e.g. 10:1, so if a person deposit 1 of TokenX will get 10 of my tokens. The person should also be able to withdraw his tokens and I must not be able to control the deposits.

More accurate example if someone deposits 1 USDC will get 10 Tokens and this is always fixed

I don't know if this is possible, I thought cloning the WETH contract and change it a bit but I feel the deposit feature works only with ETH not with tokens

Answer 1

You should use the approve + transferFrom combination. So it would work something like this:

1. User adds your contract allowance to withdraw 10 of his tokenA (with the approve function)

2. User calls your contract's exchange function (or whatever it's called). This function: a) withdraws the 10 tokenA from user's wallet (transferFrom) and b) sends 1 tokenB to the same user's wallet.

And vice versa, for the reverse.

Answer 2

Untested quick example to show you how the concept works:

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";

interface IUSDC {
  transferFrom(address, address, uint)
}

contract peggedToken is ERC20 {
  address usdcContract = 0xa0b86991c6218b36c1d19d4a2e9eb0ce3606eb48;
  
  constructor ERC20("PeggedToken", "PT") {
  }

  function getPeggedToken(uint usdcIn) {
    IUSDC(usdcContract).transferFrom(msg.sender, address(this), usdcIn);
    _mint(msg.sender, usdcIn*10);
  }
}

This is the basic idea. User will need to make an approve call to the USDC contract directly, first, with the amount of usdcIn, and the address of this contract.