public static class StringExtensions
{
    public static bool ContainsAnySymbol(
        this string str,
        IEnumerable<char> symbols) =>
        str.Intersect(symbols).Any();

    public static bool ContainsAllSymbols(
        this string str,
        IEnumerable<char> symbols) =>
        symbols.ToHashSet().IsSubsetOf(str.ToHashSet());
}

class MyClass;

abstract class MyAbstractClass;

struct MyStruct;

interface IMarkerInterface;

int[] intArray = [1, 2, 3];
List<int> intList = [4, 5, 6];
ImmutableArray<object> emptyCollection = [];

string[] vowels = ["a", "e", "i", "o", "u"];
string[] consonants = ["b", "c", "d", "f", "g", "h", "j", "k", "l", "m",
    "n", "p", "q", "r", "s", "t", "v", "w", "x", "z"];
string[] alphabet = [.. vowels, .. consonants, "y"];

record Message(string Sender, string Content);

List<Message> messages = [
    new Message(Sender: "Alex", Content: "abc"),
    new Message(Sender: "Bob", Content: "123"),
    new Message(Sender: "Jim", Content: "=-+")
];

var messagesBySender = messages
    .ToDictionary(x => x.Sender, x => x);

List<Message> messages = [
    new Message(Sender: "Alex", Content: "abc"),
    // ...
    new Message(Sender: "Alex", Content: "xyz")
];

System.ArgumentException: An item with the same key has already been added. Key: Alex

var messagesBySender = messages
    .ToLookup(x => x.Sender);

Lookup

Dictionary