What’s the difference between == and ===?

Swift version: 5.4

Paul Hudson @twostraws June 1st 2019

Swift gives us two equality operators, == and ===, that do slightly different things. You will almost certainly need to use both of them so it’s worth taking the time to learn them.

First, == is the equality operator, which tests that two things are equal for whatever definition of “equal” those things use. For example, 5 == 5 is true because there == means an integer comparison, and the same is true for other built-in value types such as strings, booleans, and doubles.

Things get more complicated when == is used with a struct you built, because by default they cannot be compared – you need to make them conform to the Equatable protocol.

In comparison, === is the identity operator, which checks whether two instances of a class point to the same memory. This is different from equality, because two objects that were created independently using the same values will be considered equal using == but not === because they are different objects.

The === operator is available only when using classes because structs are designed so they are always uniquely referenced.