Reserving capacity

Dictionary and sequence now have the capacity to explicitly, unambiguously reserve capacity.

Suppose you have a sequence of friends with an initial capacity of 4:

friends.capacity  // 4

You can now reserve the capacity by doing this:

friends.reserveCapacity(20)

This reserves a minimum of 20 segments of capacity:

friends.capacity // 20

Reallocating memory to objects can be an expensive task, and if you have an idea about how much space it will require to store an object, then using reserveCapacity(_:) can be an easy and simple way to increase performance.

Swift 4 brings in a number of modifications to the Dictionary, 12 to be exact as per the official Apple developers guide, and a number of additions that we will discuss in subsequent sections: