Add a library for handling short strings in a gas efficient way

[Amxx]

Allow string → bytes32 with string storage fallback.

This provides an effective way to store short strings (<32chars) in immutable storage.

PR Checklist

• Tests
• Documentation
• Changeset entry (run npx changeset add)

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🦋 Changeset detected

Latest commit: fb9aac4

The changes in this PR will be included in the next version bump.

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Name	Type
openzeppelin-solidity	Minor

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[frangio]

I'm not convinced by the naming. How do we expect this function be used? As a method with using for?

[Amxx]

I was thinking

contract NamedContract {
    ShortStrings.ShortString private immutable _name;
    string private _nameFallback;
    
    constructor(string memory name_) {
        _name = ShortStrings.setWithFallback(name_, _nameFallback);
    }
    
    function name() public view returns (string memory) {
        return ShortStrings.getWithFallback(_name, _nameFallback);
    }
}

How would you do it?

[Amxx]

would you prefer

constructor(string memory name_) {
    _name = name_.toShortStringWithFallback(_nameFallback);
}
function name() public view returns (string memory) {
    return _name.toStringWithFallback(_nameFallback);
}

?

[frangio]

I was thinking the same. Those are good.

We should add that as an example snippet in the docs (without an underscore suffix though 😕).

[frangio]

Please review the PR title according to the guidelines: https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/GUIDELINES.md#pull-requests

[frangio]

LGTM!