Cross Contract
Let go into this exercise.
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// SPDX-License-Identifier: BUSL-1.1
pragma solidity ^0.8.13;
contract CrossContract {
/**
* The function below is to call the price function of PriceOracle1 and PriceOracle2 contracts below and return the lower of the two prices
*/
function getLowerPrice(
address _priceOracle1,
address _priceOracle2
) external view returns (uint256) {
// your code here
}
}
contract PriceOracle1 {
uint256 private _price;
function setPrice(uint256 newPrice) public {
_price = newPrice;
}
function price() external view returns (uint256) {
return _price;
}
}
contract PriceOracle2 {
uint256 private _price;
function setPrice(uint256 newPrice) public {
_price = newPrice;
}
function price() external view returns (uint256) {
return _price;
}
}
Problem Analysis
There are two Oracle contracts provide price service, each can set and get a price. The mission is get two prices, compare, and return the lower one.
The key is how to instantiate a contract which already deployed on blockchain.
We use contract name and address to instantiate a contract.
Coding
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contract CrossContract {
/**
* The function below is to call the price function of PriceOracle1 and PriceOracle2 contracts below and return the lower of the two prices
*/
function getLowerPrice(
address _priceOracle1,
address _priceOracle2
) external view returns (uint256) {
// your code here
PriceOracle1 priceOracle1 = PriceOracle1(_priceOracle1);
PriceOracle2 priceOracle2 = PriceOracle2(_priceOracle2);
uint256 price1 = priceOracle1.price();
uint256 price2 = priceOracle2.price();
return price1 < price2 ? price1 : price2;
}
}
Test
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➜ CrossContract git:(main) ✗ forge test -vvv
[⠊] Compiling...
[⠃] Compiling 19 files with Solc 0.8.25
[⠊] Solc 0.8.25 finished in 895.54ms
Compiler run successful!
Ran 1 test for test/CrossContract.t.sol:CrossContractTest
[PASS] testGetLowerPrice() (gas: 74161)
Suite result: ok. 1 passed; 0 failed; 0 skipped; finished in 4.70ms (355.29µs CPU time)
Ran 1 test suite in 211.40ms (4.70ms CPU time): 1 tests passed, 0 failed, 0 skipped (1 total tests)
Great, we passed 1 test cases!
Reference: Solidity Exercise - CrossContract
