Swift lazy observe and mutate pattern for arrays
$begingroup$
I am using the following pattern in my code.
It works. But, it feels as though it is on the edge of what should work!
Should I consider an alternative?
I have an array in my class that maps an underlying data array. This is the sort of thing for which I could use a lazy sequence. However, I don't want to re-evaluate every time an element is accessed. So, I lazily load my array, then track the data array with KVO. I also want my top-level array to be observable. I mutate that with a mutableArrayValue.
I have mocked up a simple working example of the pattern below.
mutableArrayValue would usually cause a lazy var to initialise, but it seems OK to call it during an initialisation.
Setting up an observation on a lazy var does not cause it to initialise. I don't get a call here even though the effective setting of the array comes after the observation is created.
import Cocoa
class LazyData: NSObject
{
@objc dynamic lazy var units: [Int] = {
print("Loading units")
return [1,2,3,4,5,6] }()
}
class Lazy: NSObject
{
let data: LazyData
init(with data: LazyData) {
self.data = data
}
var unitsObservation: NSKeyValueObservation?
func tenTimes(_ input: Int) -> Int { return 10 * input }
@objc dynamic lazy var tens: [Int] = {
print("Loading tens")
let tenProxy = mutableArrayValue(forKeyPath: #keyPath(Lazy.tens))
unitsObservation = data.observe(.units) { object, change in
if change.kind == .insertion {
for insertionIndex in change.indexes! {
let ten = self.tenTimes(object.units[insertionIndex])
tenProxy.insert(ten, at: insertionIndex)
}
}
}
return data.units.map { tenTimes($0) }
}()
}
var lazyData = LazyData()
var lazy = Lazy(with: lazyData)
print(lazy.tens)
let lazyDataProxy = lazyData.mutableArrayValue(forKeyPath: #keyPath(LazyData.units))
lazyDataProxy.insert(9, at: 0)
print(lazy.tens)
swift cocoa
edited 16 mins ago
Jamal♦
30.4k11121227
asked 10 hours ago
GilesGiles
101
New contributor
Giles is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
add a comment |
$begingroup$
I am using the following pattern in my code.
It works. But, it feels as though it is on the edge of what should work!
Should I consider an alternative?
I have an array in my class that maps an underlying data array. This is the sort of thing for which I could use a lazy sequence. However, I don't want to re-evaluate every time an element is accessed. So, I lazily load my array, then track the data array with KVO. I also want my top-level array to be observable. I mutate that with a mutableArrayValue.
I have mocked up a simple working example of the pattern below.
mutableArrayValue would usually cause a lazy var to initialise, but it seems OK to call it during an initialisation.
Setting up an observation on a lazy var does not cause it to initialise. I don't get a call here even though the effective setting of the array comes after the observation is created.
import Cocoa
class LazyData: NSObject
{
@objc dynamic lazy var units: [Int] = {
print("Loading units")
return [1,2,3,4,5,6] }()
}
class Lazy: NSObject
{
let data: LazyData
init(with data: LazyData) {
self.data = data
}
var unitsObservation: NSKeyValueObservation?
func tenTimes(_ input: Int) -> Int { return 10 * input }
@objc dynamic lazy var tens: [Int] = {
print("Loading tens")
let tenProxy = mutableArrayValue(forKeyPath: #keyPath(Lazy.tens))
unitsObservation = data.observe(.units) { object, change in
if change.kind == .insertion {
for insertionIndex in change.indexes! {
let ten = self.tenTimes(object.units[insertionIndex])
tenProxy.insert(ten, at: insertionIndex)
}
}
}
return data.units.map { tenTimes($0) }
}()
}
var lazyData = LazyData()
var lazy = Lazy(with: lazyData)
print(lazy.tens)
let lazyDataProxy = lazyData.mutableArrayValue(forKeyPath: #keyPath(LazyData.units))
lazyDataProxy.insert(9, at: 0)
print(lazy.tens)
swift cocoa
edited 16 mins ago
Jamal♦
30.4k11121227
asked 10 hours ago
GilesGiles
101
New contributor
Giles is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
add a comment |
$begingroup$
I am using the following pattern in my code.
It works. But, it feels as though it is on the edge of what should work!
Should I consider an alternative?
I have an array in my class that maps an underlying data array. This is the sort of thing for which I could use a lazy sequence. However, I don't want to re-evaluate every time an element is accessed. So, I lazily load my array, then track the data array with KVO. I also want my top-level array to be observable. I mutate that with a mutableArrayValue.
I have mocked up a simple working example of the pattern below.
mutableArrayValue would usually cause a lazy var to initialise, but it seems OK to call it during an initialisation.
Setting up an observation on a lazy var does not cause it to initialise. I don't get a call here even though the effective setting of the array comes after the observation is created.
import Cocoa
class LazyData: NSObject
{
@objc dynamic lazy var units: [Int] = {
print("Loading units")
return [1,2,3,4,5,6] }()
}
class Lazy: NSObject
{
let data: LazyData
init(with data: LazyData) {
self.data = data
}
var unitsObservation: NSKeyValueObservation?
func tenTimes(_ input: Int) -> Int { return 10 * input }
@objc dynamic lazy var tens: [Int] = {
print("Loading tens")
let tenProxy = mutableArrayValue(forKeyPath: #keyPath(Lazy.tens))
unitsObservation = data.observe(.units) { object, change in
if change.kind == .insertion {
for insertionIndex in change.indexes! {
let ten = self.tenTimes(object.units[insertionIndex])
tenProxy.insert(ten, at: insertionIndex)
}
}
}
return data.units.map { tenTimes($0) }
}()
}
var lazyData = LazyData()
var lazy = Lazy(with: lazyData)
print(lazy.tens)
let lazyDataProxy = lazyData.mutableArrayValue(forKeyPath: #keyPath(LazyData.units))
lazyDataProxy.insert(9, at: 0)
print(lazy.tens)
swift cocoa
edited 16 mins ago
Jamal♦
30.4k11121227
asked 10 hours ago
GilesGiles
101
New contributor
Giles is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
I am using the following pattern in my code.
It works. But, it feels as though it is on the edge of what should work!
Should I consider an alternative?
I have an array in my class that maps an underlying data array. This is the sort of thing for which I could use a lazy sequence. However, I don't want to re-evaluate every time an element is accessed. So, I lazily load my array, then track the data array with KVO. I also want my top-level array to be observable. I mutate that with a mutableArrayValue.
I have mocked up a simple working example of the pattern below.
mutableArrayValue would usually cause a lazy var to initialise, but it seems OK to call it during an initialisation.
Setting up an observation on a lazy var does not cause it to initialise. I don't get a call here even though the effective setting of the array comes after the observation is created.
import Cocoa
class LazyData: NSObject
{
@objc dynamic lazy var units: [Int] = {
print("Loading units")
return [1,2,3,4,5,6] }()
}
class Lazy: NSObject
{
let data: LazyData
init(with data: LazyData) {
self.data = data
}
var unitsObservation: NSKeyValueObservation?
func tenTimes(_ input: Int) -> Int { return 10 * input }
@objc dynamic lazy var tens: [Int] = {
print("Loading tens")
let tenProxy = mutableArrayValue(forKeyPath: #keyPath(Lazy.tens))
unitsObservation = data.observe(.units) { object, change in
if change.kind == .insertion {
for insertionIndex in change.indexes! {
let ten = self.tenTimes(object.units[insertionIndex])
tenProxy.insert(ten, at: insertionIndex)
}
}
}
return data.units.map { tenTimes($0) }
}()
}
var lazyData = LazyData()
var lazy = Lazy(with: lazyData)
print(lazy.tens)
let lazyDataProxy = lazyData.mutableArrayValue(forKeyPath: #keyPath(LazyData.units))
lazyDataProxy.insert(9, at: 0)
print(lazy.tens)
swift cocoa
swift cocoa
edited 16 mins ago
Jamal♦
30.4k11121227
asked 10 hours ago
GilesGiles
101
New contributor
Giles is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 16 mins ago
Jamal♦
30.4k11121227
asked 10 hours ago
GilesGiles
101
New contributor
Giles is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 16 mins ago
Jamal♦
30.4k11121227
edited 16 mins ago
Jamal♦
30.4k11121227
edited 16 mins ago
Jamal♦
30.4k11121227
30.4k11121227
asked 10 hours ago
GilesGiles
101
New contributor
Giles is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 10 hours ago
GilesGiles
101
asked 10 hours ago
GilesGiles
101
101
New contributor
Giles is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
Giles is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Giles is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |
add a comment |
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