Computed properties vs methods
When picking between a computed property versus a method in Swift, I choose a property when:
- The API I’m defining returns some form of information about an object or value’s state.
- Its body can be executed in
O(1)time.
extension TodoItem {
// Returning information about an object/value's state in
// constant time = property.
var isCompleted: Bool {
return state == .completed
}
// Returning a new value after applying a mutation = method.
func completed() -> TodoItem {
var item = self
item.state = .completed
return item
}
// Returning information, but in a way that's slower than
// constant time (O(N), where N is the number of attachments
// in this case) = method.
func attachmentTags() -> Set<Tag> {
return attachments.reduce([]) { tags, attachment in
tags.union(attachment.tags)
}
}
}
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