Looking at Immutable Data with Optics

Immutability is a concept supported in Kotlin that we usually implement using data classes and read only properties. Working with complex nested immutable structures can be a bit unfriendly with this language, given how nested calls to the copy constructor lead to hardly understandable codebases. In this talk, we will learn about optics, and how we can use and compose them to create highly reusable paths to update our nested data structures.

- Intro into Optics (Lens, Prism, Optional)
- Composing Optics
- Separating path vs logic (includes DSL)
- Outro: more optics (Traversal / Fold)

The video for this talk can be found here: https://www.youtube.com/watch?v=Q7GtlbAFGCc

This talk is part of the 47 Degrees Academy and was given by Simon Vergauwen.

Transcript

1. Goals Rationale Creating
Optics Using
Optics
2. Target
platform:
JVM Running
on
Arrow
v.
0.10.5 Running
on
Kotlin
v.
1.3.50 data
class
Street(val
number:
Int,
val
name:
String) data
class
Address(val
city:
String,
val
street:
Street) data
class
Company(val
name:
String,
val
address:
Address) data
class
Employee(val
name:
String,
val
company:
Company)
3. Target
platform:
JVM Running
on
Arrow
v.
0.10.5 Running
on
Kotlin
v.
1.3.50 val
simon
=
Employee("Simon",
Company("Kategory", 





































Address("Functional
city",
Street(42,
"lambda
street")) 




































)) val
updated
=
simon.copy( 



company
=
simon.company.copy( 







address
=
simon.company.address.copy( 











street
=
simon.company.address.street.copy( 















name
= 



















simon.company.address.street.name.toUpperCase() 











) 







) 



)
4. -val
updated
=
simon.copy(
 -

company
=
simon.company.copy(
 -



address
=
simon.company.address.copy(
 -





street
=
simon.company.address.street.copy(
 -







name
=
 -







simon.company.address.street.name.toUpperCase()
 -





)
 -



)
 -

)
 -)
 
 +val
lens
=
Employee.company.address.street.name
 +val
updated
=
lens.modify(simon,
String::toUpperCase)
5. Target
platform:
JVM Running
on
Arrow
v.
0.10.5 Running
on
Kotlin
v.
1.3.50 sealed
class
Json data
class
JsString(val
string:
String):
Json() data
class
JsInteger(val
integer:
Long):
Json() data
class
JsNumber(val
number:
String):
Json() data
class
JsBool(val
bool:
Boolean):
Json() data
class
JsArray(val
array:
List<Json>):
Json() data
class
JsObject(val
objects:
Map<String,
Json>):
Json() object
JsNull:
Json()
8. Lens
=
get
+
copy Target
platform:
JVM Running
on
Arrow
v.
0.10.5 Running
on
Kotlin
v.
1.3.50 data
class
JsString(val
string:
String)
{ 



companion
object
{ 







val
string:
Lens<JsString,
String>
=
Lens( 











get
=
JsString::string, 











set
=
{
js,
string
->
js.copy(string)
} 







) 



} }
9. +@optics
 data
class
JsString(val
string:
String)
:
Json()
{
 

companion
object
{
 -



val
string:
Lens<JsString,
String>
=
Lens(
 -





get
=
JsString::string,
 -





set
=
{
js,
string
->
js.copy(string)
}
 -



)
 

}
 }
10. Target
platform:
JVM Running
on
Arrow
v.
0.10.5 Running
on
Kotlin
v.
1.3.50 val
example
=
JsString("Blue-Rectangle") JsString.string.get(example)
11. Target
platform:
JVM Running
on
Arrow
v.
0.10.5 Running
on
Kotlin
v.
1.3.50 val
example
=
JsString("Blue-Rectangle") JsString.string.modify(example)
{
it.reversed()
} JsString.string.set(example,
"Green-Rectangle")
16. Target
platform:
JVM Running
on
Arrow
v.
0.10.5 Running
on
Kotlin
v.
1.3.50 sealed
class
Json data
class
JsString(val
string:
String):
Json() data
class
JsInteger(val
integer:
Long):
Json() data
class
JsNumber(val
number:
String):
Json() data
class
JsBool(val
bool:
Boolean):
Json() data
class
JsArray(val
array:
List<Json>):
Json() data
class
JsObject(val
objects:
Map<String,
Json>):
Json() object
JsNull:
Json()
17. Target
platform:
JVM Running
on
Arrow
v.
0.10.5 Running
on
Kotlin
v.
1.3.50 sealed
class
Json data
class
JsString(val
string:
String):
Json() object
JsNull:
Json()
18. Prism
=
when
+
constructor Target
platform:
JVM Running
on
Arrow
v.
0.10.5 Running
on
Kotlin
v.
1.3.50 fun
Json.getOrModify():
Either<Json,
JsString>
= 



when
(this)
{ 







is
JsString
->
Either.Right(this) 







else
->
Either.Left(this) 



} fun
JsString.asJson():
Json
= 



this
19. Prism
=
when
+
constructor Target
platform:
JVM Running
on
Arrow
v.
0.10.5 Running
on
Kotlin
v.
1.3.50 fun
Json.getOrModify():
Either<Json,
JsString>
= 



when
(this)
{ 







is
JsString
->
Either.Right(this) 







else
->
Either.Left(this) 



} fun
JsString.reverseGet():
Json
= 



this fun
Json.Companion.jsString():
Prism<Json,
JsString>
= 



Prism( 







getOrModify
=
{
it.getOrModify()
}, 







reverseGet
=
{
it.reverseGet()
}
20. Target
platform:
JVM Running
on
Arrow
v.
0.10.5 Running
on
Kotlin
v.
1.3.50 @optics sealed
class
Json @optics data
class
JsString(val
string:
String):
Json() object
JsNull:
Json()
27. Prism#modify Target
platform:
JVM Running
on
Arrow
v.
0.10.5 Running
on
Kotlin
v.
1.3.50 import
arrow.optics.Prism import
arrow.core.Either fun
<S,
A>
Prism<S,
A>.modify(s:
S,
f:
(A)
->
A):
S
= 

when(val
result
=
getOrModify(s))
{ 



is
Either.Right
->
reverseGet(f(result.b)) 



is
Either.Left
->
result.a 

}
29. -val
example
=
JsString("Blue-Rectangle")
 +val
example:
Json
=
JsString("Blue-Rectangle")
30. Target
platform:
JVM Running
on
Arrow
v.
0.10.5 Running
on
Kotlin
v.
1.3.50 val
json:
Json
=
JsString("Blue-Rectangle") val
updated
=
when(json)
{ 

is
JsString
->
json.copy(json.string.reversed()) 

else
->
json
 }
31. Optional
=
Lens
+
Prism -val
updated
=
when(example)
{
 -

is
JsString
->

example.copy(example.string.reversed())
 -

else
->
example

 -}
 +val
optional:
Optional<Json,
String>
=
 +

Json.jsString
compose
JsString.string
32. Target
platform:
JVM Running
on
Arrow
v.
0.10.5 Running
on
Kotlin
v.
1.3.50 sealed
class
Json data
class
JsArray(val
array:
List<Json>):
Json() object
JsNull:
Json()
33. Target
platform:
JVM Running
on
Arrow
v.
0.10.5 Running
on
Kotlin
v.
1.3.50 val
array:
Json
=
JsArray(listOf( 

JsString("Blue-Rectangle"), 

JsString("Green-Rectangle") ))
34. Target
platform:
JVM Running
on
Arrow
v.
0.10.5 Running
on
Kotlin
v.
1.3.50 val
json:
Json
=
JsArray(listOf(JsString("Blue-Rectangle"),
JsString("Green-Rectangle"))) when(json)
{ 

is
JsArray
->
json.array.copy(json.array.map
{
value
-> 



when(value)
{ 





is
JsString
->
value.copy(value.string.reversed()) 





else
->
value 



} 

}) 

else
->
json }
35. -when(json)
{
 -

is
JsArray
->
json.array.copy(json.array.map
{
value
->
 -



when(value)
{
 -





is
JsString
->
value.copy(value.string.reversed())
 -





else
->
value
 -



}
 -

})
 -

else
->
json
 -}
 +val
path:
Traversal<Json,
String>
=
 +

Json.jsArray
compose
 +



JsArray.array
compose
 +



ListExtensions.traversal()
compose
 +



Json.jsString
compose
 +



JsString.string
36. -val
path:
Traversal<Json,
String>
=
 -

Json.jsArray
compose
 -



JsArray.array
compose
 -



ListExtensions.traversal()
compose
 -



Json.jsString
compose
 -



JsString.string
 +val
path
=
 +

Json.jsArray
 +



.array
 +



.every(ListExtensions.traversal())
 +



.jsString
 +



.string
37. val
path
=
 -

Json.jsArray
 -



.array
 


Json.array
 




.every(ListExtensions.traversal())
 -




.jsString
 -




.string
 




.string
43. OBS
07
Goodbye
44. Q&A