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Compiling contracts that uses ConnectOracle.sol requires the viaIR feature. For Foundry/Forge, this can be done by using the --via-ir flag. The relevant methods for other tools may vary.

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Foundry

For this tutorial, we will be using Foundry toolkit to develop, compile, and deploy our contracts. If you do not have Foundry installed, follow the Foundry installation instructions.

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Setup

First, we need to create a new directory for our project. 
mkdir connect-oracle
cd connect-oracle
Next, we will initialize a new Foundry project side that directory. 
forge init
Once the project is initialized, we can proceed to installing the required dependencies needed for this tutorial. In this case, we only need Initia’s EVM contracts. 
forge install initia-labs/initia-evm-contracts

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Implementing the Contract

Before writing our contract, we first need to rename the template contract to NewInitiaERC20.sol 
mv src/Counter.sol src/Oracle.sol
We then update the contract from the template to be our oracle contract. Start by importing the IConnectOracle interface from the @initia/initia-evm-contracts package.
src/Oracle.sol
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;

import "initia-evm-contracts/src/interfaces/IConnectOracle.sol";
Next, we declare the variables that we will use in the contract’s operations.
  • connect: The interface of the ConnectOracle contract
  • currencyPair: The variable that stores the currency pair response from ConnectOracle
  • price The variable that stores the single pair price response from ConnectOracle
  • prices The variable that stores the multiple pair prices response from ConnectOracle
src/Oracle.sol
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;

import "initia-evm-contracts/src/interfaces/IConnectOracle.sol";

contract Oracle {

    IConnectOracle immutable public connect;

    string public currencyPairs;
    IConnectOracle.Price public price;
    IConnectOracle.Price[] public prices;
We then need to define the constructor for our contract. This will be used to initialize the contract with the ConnectOracle contract address.
src/Oracle.sol
    constructor(address connect_) {
        connect = IConnectOracle(connect_);
    }
Once the constructor is implement, we move on to defining the different functions that our contract will have
  • oracle_get_all_currency_pairs: This function will return all of the asset pairs currently supported by Connect
  • oracle_get_price: This function will return the price of a single asset pair
  • oracle_get_prices: This function will return the price of multiple asset pairs
src/Oracle.sol
    function oracle_get_all_currency_pairs() external {
        currencyPairs = connect.get_all_currency_pairs();
    }

    function oracle_get_price() external {
        string memory base = "BTC";
        string memory quote = "USD";
        price = connect.get_price(base, quote);
    }

    function oracle_get_prices() external {
        string[] memory pair_ids = new string[](2);
        pair_ids[0]= "BTC/USD";
        pair_ids[1]= "ETH/USD";
        
        IConnectOracle.Price[] memory memoryPrices = connect.get_prices(pair_ids);

        // Clear the existing storage array
        delete prices;

        // Copy each element from memory to storage
        for (uint256 i = 0; i < memoryPrices.length; i++) {
            prices.push(memoryPrices[i]);
        }
    }
Our complete contract will then look like this:
src/Oracle.sol
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;

import "initia-evm-contracts/src/interfaces/IConnectOracle.sol";

contract Oracle {

    IConnectOracle immutable public connect;

    string public currencyPairs;
    IConnectOracle.Price public price;
    IConnectOracle.Price[] public prices;

    constructor (address _connect) {
        connect = IConnectOracle(_connect);
    }

    function oracle_get_all_currency_pairs() external {
        currencyPairs = connect.get_all_currency_pairs();
    }

    function oracle_get_price() external {
        string memory base = "BTC";
        string memory quote = "USD";
        price = connect.get_price(base, quote);
    }

    function oracle_get_prices() external {
        string[] memory pair_ids = new string[](2);
        pair_ids[0]= "BTC/USD";
        pair_ids[1]= "ETH/USD";
        
        IConnectOracle.Price[] memory memoryPrices = connect.get_prices(pair_ids);

        // Clear the existing storage array
        delete prices;

        // Copy each element from memory to storage
        for (uint256 i = 0; i < memoryPrices.length; i++) {
            prices.push(memoryPrices[i]);
        }
    }
}
Our contract implementation is now ready. However, if we try to compile the contract using forge compile, we will get an error. This is because the default Oracle.t.sol expects the original Oracle.sol contract to be available. To fix this, we will rename Oracle.t.sol to OracleTest.t.sol. 
mv test/Counter.t.sol test/Oracle.t.sol
We will also replace the file contents with placeholder content.
test/OracleTest.t.sol
// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.13;

import {Test, console} from "forge-std/Test.sol";

contract OracleTest is Test {

}
Now running forge compile should work without any errors. 
forge compile;

# [Expected Output]:
# [⠢] Compiling...
# [⠰] Compiling 27 files with 0.8.21
# [⠃] Solc 0.8.21 finished in 6.25s
# Compiler run successful!

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Deploying the Contract

Now that Our contract is compiled and ready, we can deploy it to the MiniEVM. To accomplish this, we will use Foundry’s forge create command 
export PRIVATE_KEY=0x...
export RPC_URL=http://...
forge create src/Oracle.sol:Oracle --private-key $PRIVATE_KEY --rpc-url $RPC_URL --constructor-args 0xc47ef2D751f64bC3FADc7dE3027fE02C94122056 --legacy

# [Expected Output]:
# No files changed, compilation skipped
# Deployer: 0xc5D26D0281e28599c7790aacc810226BBDf0E431
# Deployed to: 0xdDa3cB3675238f3264F417DF48bf559bE8704a47
# Transaction hash: 0xa3fbbbe112b2341fcbfecde5f7b5908b59b63361019370ac531ab31a043df501
To confirm that the contract was deployed successfully, we can try calling the oracle_get_all_currency_pairs function using Foundry’s cast send command. 
cast send 0xdDa3cB3675238f3264F417DF48bf559bE8704a47 \
"oracle_get_all_currency_pairs()" \
--private-key $PRIVATE_KEY \
--rpc-url $RPC_URL \

# [Expected Output]:
# blockHash               0x312c712feae5d2bb0bc69e5463767465e1270c3a48863a9e08eea94986c9da1a
# blockNumber             89847
# contractAddress         
# cumulativeGasUsed       2353429
# ...
If you then try querying the currencyPairs variable using Foundry’s cast call command, you should see the response from Connect. 
cast call 0xdDa3cB3675238f3264F417DF48bf559bE8704a47 \
"currencyPairs()" \
--rpc-url $RPC_URL

# [Expected Output]:
# {\"currency_pairs\":[{\"Base\":\"AAVE\",\"Quote\":\"USD\"},{\"Base\":\"ADA\",\"Quote\":\"USD\"},{\"Base\":\"AEVO\",\"Quote\":\"USD\"},{\"Base\":\"AGIX\",\"Quote\":\"USD\"},{\"Base\":\"ALGO\",\"Quote\":\"USD\"},{\"Base\":\"APE\",\"Quote\":\"USD\"},{\"Base\":\"APT\",\"Quote\":\"USD\"},{\"Base\":\"ARB\",\"Quote\":\"USD\"},{\"Base\":\"ARKM\",\"Quote\":\"USD\"}...