Mastering Blockchain Programming with Solidity

Creating a custom modifier using function modifiers

The modifiers are used to check the pre- and post-conditions before calling a method. Argument validation and correctness are checked with the modifiers. The function modifiers are also used to maintain the access and role-based control on the contract.

In the following example code, onlyOwner is an access modifier function used in the withdraw function. The definition says that the withdraw function can only be allowed to call from the owner address:

contract AccountContract {    address public owner;    /*     * Modifier onlyOwner definition.     */    modifier onlyOwner() {        require(msg.sender == owner, "not owner");        _;  //Rest of the function body execution    }    /* * The deployer of the contract would become ...