I was studying the uniswap V2 smart contract, and I saw that in the constructor part, using assembly, the value of the chainId was set in a variable.

    constructor() public {
        uint chainId;
        assembly {
            chainId := chainid
        DOMAIN_SEPARATOR = keccak256(
                keccak256('EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)'),

Is it possible to create a blockchain whose chainId will encounter overflow when the constructor is executed?

Is there a law to choose chainId for new blockchains?


1 Answer 1


ChainId has a size of 256 bits, meaning there can not be a number that is larger than that in blockchain saved in a single variable. So to answer your question, no there can not be any overflow.

The following article might help: https://eips.ethereum.org/EIPS/eip-1344

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