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Constant vs Immutable

  1. constant: Declares a constant that must be initialized at the time of declaration and cannot be altered thereafter.

  2. immutable: Declares a constant that can be initialized either at the time of declaration or within the constructor, and cannot be altered after deployment.

  3. variable: Declares a variable that can be assigned and modified at any stage of the contract lifecycle.

The following examples illustrate three variables defined with different modifiers.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.4;

contract ConstantExample {
uint256 public constant FIXED_VALUE = 100;

contract ImmutableExample {
uint256 public immutable SETUP_VALUE = 100;

contract VariableExample {
uint256 public dynamicValue = 100;

Recommendations for gas optimization:

🌟 Using variables consumes more gas, so avoid them if you can.

🌟 For constants that do not require modifications after deployment, defining them as immutable is optimal both functionally and in terms of gas efficiency.