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I keep reviewing code with interfaces, without seeing any reference anywhere of what contract that interface points to. For example in this contract for the popular cryptocurrency Axie Infinity:

On line 49, we see that there is an interface for the ERC20 token contract

interface IERC20 {
  event Transfer(address indexed _from, address indexed _to, uint256 _value);
  event Approval(address indexed _owner, address indexed _spender, uint256 _value);

  function totalSupply() external view returns (uint256 _supply);
  function balanceOf(address _owner) external view returns (uint256 _balance);

But no reference to which contract on the blockchain is being referenced.

  • MY Question:

    • How does this contract and other contracts know which contract the interface is referencing when compiled, when there is absolutely no contract being referenced in the code?

1 Answer 1

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It is used by the inheritance

contract ERC20 is IERC20 {
...
}

contract ERC20Detailed is ERC20, IERC20Detailed {
...
}

contract AXSToken is ERC20Detailed, ERC20GatewayWhitelist {
...
}

So by inheritance AXSToken as IERC20.

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