ShortString.sol

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.9;

// Unlike the string type, ShortString is a value type that can be made immutable.
// It supports strings of at most 32 bytes and assumes they don't contain null bytes.

type ShortString is bytes32;

error StringTooLong(string s);

function toShortString(string memory s) pure returns (ShortString) {
    bytes memory b = bytes(s);
    if (b.length > 32) {
        revert StringTooLong(s);
    }
    return ShortString.wrap(bytes32(b));
}

function shortStringLength(ShortString s) pure returns (uint) {
    uint x = uint(ShortString.unwrap(s));
    uint len = 0;
    for (uint m = 0xff << 248; m != 0; m >>= 8) {
        if (x & m == 0) {
            break;
        }
        len += 1;
    }
    return len;
}

function toString(ShortString s) pure returns (string memory) {
    bytes memory b = new bytes(32);
    uint len = shortStringLength(s);
    assembly {
        mstore(b, len)
        mstore(add(b, 32), s)
    }
    return string(b);
}

TestShortString.sol

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.9;

import './ShortString.sol';

contract TestShortString {
    ShortString immutable $name;

    constructor(string memory _name) {
        $name = toShortString(_name);
    }

    function name() public view returns (string memory) {
        return toString($name);
    }
}