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Introduction to the Solidity Programming Language

Modifiers

Learn about function modifiers in Solidity.

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Understanding modifiers

Function modifiers change the behavior of a function by adding requirements. The function body is placed wherever the special symbol _; appears in a modifier’s definition. So, if the modifier condition is met while invoking this method, the function is executed; otherwise, an exception is raised.

Here’s the syntax to declare a modifier:

C++
modifier <modifier_name>(<parameter-list>) {
   //Code to execute
   //ending with special symbol
   _;
}

Modifiers in Solidity are defined by using the modifier keyword, followed by a name and a code block. These code blocks frequently include criteria to be met for the function to be executed correctly. When a function employs a modifier, the code included within it is executed first, followed by the function itself.

Solidity
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.17;
contract Storage {
    //Declaring state variable of uint type
    uint256 public number;
    address public owner;
    constructor(){
        //Setting the owner address with the value of deployer
        owner = msg.sender;
        //Invoking a getIncrementNumber function
        incrementedNumberBy(1);
    }
    //Modifier without parameter to check owner before execution
    modifier onlyOwner(){
        require(owner == msg.sender, "not an owner");
        _;
    }
    //Modifier with parameter to validate function parameter
    modifier isGreaterThanZero(uint _num){
        require(_num > 0);
        _;
    }
    //Declaring a function to increment a value by parameter provided
    function incrementedNumberBy(uint _num) public view onlyOwner isGreaterThanZero(_num) returns(uint){
        //Local variable Nonce
        uint nonce = number +_num;
        //Return statement to return final output of number
        return nonce;
    }
}

  • Line 3: We declare a contract named Storage.

  • Lines 5–6: We declare two state variables:

    • number: We declare this state variable of the type uint256 ...