在 C# 中获得相同表达式的不同结果

Question

I am getting different results when changing from != true to == false which I thought is exactly the same.

This is my code

User user = await GetUser(id);

if (user == null || user.Orders?.Any() != true)
{
    ...
}

If I change to user.Orders?.Any() == true some of my tests return different data. Why?

Answer 1

Because user.Orders?.Any() have bool? type, because of '?' after Orders. So if user.Orders is null , then result of user.Orders?.Any() will be null and == true will be false, while != false will be true

Answer 2

Your expression is a nullable boolean expression (bool?) which means that it has 3 results: true, false, null.

That's why it is not the same != true or == false .

In your case, if the user exists and his orders are null => the expression will return "null" result. So that in case of != true it will return true and in case of == false it will return false because null != true != false .