Solidity Constructor

Definition

Constructor is a special function.

Every contract can only have one constructor.

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Execution

• Constructor is executed only one time when contract is deployed.
• It cannot be called again after deployment.
• Every contract has at most one constructor.

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Core Use

1. Initialize state variables, like owner = msg.sender.
2. Do one-time setup logic when contract is created.
3. Very important in Ownable Pattern, since it decide the first owner of the contract.

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Example

constructor() { 
    // default constructor, no parameter
}

constructor(address _owner) { 
    owner = _owner; // assign owner from argument
}

owner = msg.sender; // assign contract deployer as owner