问题
I have a list of car objects
List<Car> cars = GetMyListOfCars();
and i want to see if a car is in the list
if (cars.Contains(myCar))
{
}
what does Contains use to figure out if myCar is in the list. Does it do a "ToString()" on my car object. Does it use the Equals() method, the gethashcode()?
I see i can pass in my own IEqualityComparer to force my own implementation but just wanted to understand what it does by default.
回答1:
Straight from MSDN - List<T>.Contains:
This method determines equality by using the default equality comparer, as defined by the object's implementation of the IEquatable(Of T).Equals method for T (the type of values in the list).
This method performs a linear search; therefore, this method is an O(n) operation, where n is Count.
So in the end it depends on how T implements IEquatable.Equals(). For most objects this is going to be a reference comparison, unless overriden. Same location in memory is the same object.
回答2:
It uses Equals()
This method determines equality by using the default equality comparer, as defined by the object's implementation of the IEquatable(Of T).Equals method for T (the type of values in the list).
http://msdn.microsoft.com/en-us/library/bhkz42b3.aspx
回答3:
Contains will return true as soon as it can - that is once the first item that fits the criteria is found.
A false will be returned after all items have been iterated over.
In regards to how it does that - it will use reference equality for reference types if you do not override Equals.
来源：https://stackoverflow.com/questions/9264566/how-does-listt-contains-find-matching-items