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contract Sharer {
    function sendHalf(address payable addr) public payable returns (uint balance) {
        require(msg.value % 2 == 0, "Even value required.");
        uint balanceBeforeTransfer = address(this).balance;
        addr.transfer(msg.value / 2);
        // Since transfer throws an exception on failure and
        // cannot call back here, there should be no way for us to
        // still have half of the money.
        assert(address(this).balance == balanceBeforeTransfer - msg.value / 2);
        return address(this).balance;
    }
}

上記のコントラクトで、アサーションが失敗する / address(this).balance が (msg.value / 2) 減らないのはどの条件ですか? なぜここでアサーションが必要なのですか?

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2 に答える 2