Casting

Only use "as" when you are not sure if the cast will succeed and you are going to check the result against null, otherwise you confuse the linter.

Don’t: 🙁

Cat cat = objectThatMightBeACat as Cat; // cat might be null
cat.Meow();

Better: 😐

Cat cat = objectThatMightBeACat as Cat;
cat?.Meow();

Best: 🙂

if (objectThatMightBeACat is Cat cat)
	cat.Meow();

If you are sure of the type (an exception will be thrown if you are wrong), use the direct cast:

(Cat)objectThatImSureIsACat.Meow();

Be aware of the different intentions of LINQ selectors. Use _First _when there may be more than one matching Item; _FirstOrDefault _when there may be more than one, or possibly none. Use _Single _when there is supposed to be one and only one matching item, and _SingleOrDefault _when there is either one or none.

When using the _XXXOrDefault _variants, be sure to check for null.