[Merad]

I don't know go, but in C# I'd probably do something like the code below. The object really only needs to carry the uuid/guid, let the language type system worry about the difference between a user and post id. We just need a generic mechanism to ensure that UserId object can only be constructed from a valid type id string with type = user. For production use you'd obviously need more methods to construct it from a database tuple (mentioned elsewhere in the comments), etc.

    interface ITypeIdPrefix
    {
        static abstract string Prefix { get; }
    }

    abstract class TypeId<T>
        where T : TypeId<T>, ITypeIdPrefix, new()
    {
        public Guid Id { get; private init; }

        public override string ToString() => $"{T.Prefix}_{Id.ToBase32String()}";
        // Override GetHashcode(), Equals(), etc.

        public static bool TryParse(string s, out T? result)
        {
            if (!s.StartsWith(T.Prefix) || !TrySplitStringAndParseBase32ToGuid(s, out var id))
            {
                result = default;
                return false;
            }

            result = new T { Id = id };
            return true;
        }
    }

    class UserId : TypeId<UserId>, ITypeIdPrefix
    {
        public static string Prefix => "user";
    }

    class PostId : TypeId<PostId>, ITypeIdPrefix
    {
        public static string Prefix => "post";
    }