Solidity msg.value – How is msg.value Sent in a Contract?

contract-designremixsolidity

I'm wondering how exactly "msg.value" works, like here in this example taken from https://solidity-by-example.org/hacks/self-destruct

How can the deposit function require msg.value to eqaul 1 ether when there are no arguments for the function? In other words, how does this contract/function take in msg.value? Is msg.value sent when it is deployed?

    uint public targetAmount = 7 ether;
    address public winner;

    function deposit() public payable {
        require(msg.value == 1 ether, "You can only send 1 Ether");

        uint balance = address(this).balance;
        require(balance <= targetAmount, "Game is over");

        if (balance == targetAmount) {
            winner = msg.sender;
        }
    }

    function claimReward() public {
        require(msg.sender == winner, "Not winner");

        (bool sent, ) = msg.sender.call{value: address(this).balance}("");
        require(sent, "Failed to send Ether");
    }
}

Best Answer

msg.value is included along with the transaction, you can read this part of the Solidity documentation: https://docs.soliditylang.org/en/v0.8.14/units-and-global-variables.html?#special-variables-and-functions Thus, there is no reason to include it in the function parameters.

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