Just one more essential Solidity keyword, and then we are ready to create our own ERC20 token.
Although we can use an if statement to check if inputs to a function are valid, or the correct msg.sender is calling the function, the elegant way is to use the require statement. The require statement forces the transaction to revert if some condition is not met.
Example code:
contract Require01 {
function mustNotBeFive(uint256 x) public pure returns (uint256) {
require(x != 5, "five is not valid");
return x * 2;
}
}What if you want to ensure that only the owner of the contract can make a specific change to it?
Example:
contract OnlyOwner {
address owner;
uint256 public magicNumber;
constructor(address _owner, uint256 _magicNumber) {
owner = _owner;
magicNumber = _magicNumber;
}
function updateMagicNumber(uint256 _number) public {
require(owner == msg.sender, "Sender must be owner");
magicNumber = _number;
}
}