Store string as immutable

Question

I want to deploy an nft contract and i want to enter URI in constructor:

string immutable i_uri;

constructor(string memory name, string memory symbol, string memory uri) ERC721(name,symbol)  {
    i_uri = uri;
}

But i got this error : Immutable variables cannot have a non-value type.

What is the problem?? i haven't same problem with uint,address and etc.

Answer 1

From the documentation:

Not all types for constants and immutables are implemented at this time. The only supported types are strings (only for constants) and value types.

not implemented, use constant instead.

Answer 2

The issue is that constant/immutable variables have their values defined during compilation and deployment, therefore I don't see a way to change them programmatically. Instead you could use a private variable.

pragma solidity ^0.8.0;

contract Example {
    bytes private i_uri;

    constructor(string memory name, string memory symbol, string memory uri) {
        i_uri = abi.encodePacked(uri);
    }

    function getURI() public view returns (string memory) {
        return string(i_uri);
    }
}

NOTE: Imutable is outdated, better to use contstant (For solidity ^0.8.0)