I am learning about importing contracts and noticed with the following contract there is an external interface function with no code block. Where does this code come from?
function version() external view returns (uint256);
Solidity Interfaces – How to Find the Code of an External Interface Function Using ABI
abichainlinkinterfacessolidity
Related Solutions
So, I figured out a solution.
Step 1 - brownie pm install [ORGANIZATION]/[REPOSITORY]@[VERSION]. Do this in your terminal. In my case, it'll be
brownie pm install smartcontractkit/chainlink-brownie-contracts@0.2.2
brownie pm install OpenZeppelin/openzeppelin-contracts@4.4.0
Step 2 - Add these in your VSCode settings,
"solidity.remappings": [
"@chainlink/=/Users/<USERNAME>/.brownie/packages/smartcontractkit/chainlink-brownie-contracts@0.2.2",
"@openzeppelin/=/Users/<USERNAME>/.brownie/packages/OpenZeppelin/openzeppelin-contracts@4.4.0"
]
All the versions are the latest as of 12-Dec-2021
Lastly to check all of your installed packages just type
brownie pm list in your terminal. In my case, it looks something like this.
VOILA!
For your randomness example it is important to know that Solidity generates getters for all public variables. In the governance contract there is a public variable randomness which generates the mentioned function as a getter: https://github.com/alphachainio/chainlink-lottery/blob/master/ethereum/contracts/Governance.sol#L6.
In general Solidity does not perform any check if a contract implements a specific interface when casting it to that interface. More info on this can be found here: How is an interface initialised? (there are quite some other questions also explaining this ;) )
Best Answer
This is the interface definition in Solidity docs
One way to know the source code is know a address of an interface deployed on a network which has its code verified.
Talking specifically about the
AggregatorV3Interface.sol, there are one implementation for each data feed, for example:is the data feed ETH/USD on Ethereum testnet Kovan network.
If you go to the implementation address 0x9326BFA02ADD2366b30bacB125260Af641031331 on Kovan, you will find the source code.
Check it out the Data Feeds API Reference for more information about the AggregatorV3Interface and the addresses of Ethereum Data Feeds.