How Copy-on-Write Works in Swift Fast AF

Swift provides a powerful tool for optimizing performance and reducing memory usage called copy-on-write. This technique allows multiple copies of a value to be shared until one of the copies needs to be modified, at which point a copy is made to avoid modifying the original value.

One common type in Swift that utilizes copy-on-write is the Array. When an Array is assigned to a new variable or passed as an argument to a function, the Array is actually shared between the two references. This means that any changes made to the Array through one reference will be reflected in the other reference, since they are both pointing to the same underlying data.

Here is an example of how copy-on-write works with Arrays in Swift:

var originalArray = [1, 2, 3]
var copyArray = originalArray

// Both originalArray and copyArray point to the same underlying data
print(originalArray) // Output: [1, 2, 3]
print(copyArray) // Output: [1, 2, 3]

// Now we modify the copyArray
copyArray[0] = 4

// The originalArray is not modified, but the copyArray now has a different value
print(originalArray) // Output: [1, 2, 3]
print(copyArray) // Output: [4, 2, 3]

As you can see, even though we modified the copyArray, the originalArray remained unchanged. This is because a copy of the Array was made when the modification occurred, allowing the originalArray to remain unchanged.

It’s important to note that copy-on-write is not always the most efficient option. If an Array is being modified frequently, it may be more efficient to make a copy upfront to avoid the overhead of constantly making copies.

In conclusion, copy-on-write is a powerful technique in Swift that allows multiple references to a value to be shared until one of the references needs to be modified. This is especially useful for optimizing performance and reducing memory usage when working with Arrays. Understanding how copy-on-write works is crucial for writing efficient and effective code in Swift.