问题
This is a followup question on another question I asked yesterday.
How can I build a nested list using builder pattern?
Credit to: Pelocho for giving nice answer.
I used this Tutorial to do a type safe graphQL query builder:
What I want to do now is to simplify what I made And I know that kotlin must have some nice features to do that.
Right now I have to invoke functions when I want to add an entity to my query:
fun main() {
events{
title() // I don't like to do () when it is an edge case
}
}
I am wondering if it is posible to do something different, and more simple, like:
fun main() {
events{
title // this is much nicer
}
}
But if it is not possible then it is ok just to reduce the amount of characters with an operator overloading like eg. unaryPlus
fun main() {
events{
+title // this is also nicer
}
}
My code that I have now has a class called Query where I put the method:
operator fun Query.unaryPlus() {
visitEntity(this,{})
}
But it does not seem to work for me.
All my code is here.
interface Element {
fun render(builder: StringBuilder, indent: String)
}
@DslMarker //Domain Specific Language
annotation class GraphQLMarker
@GraphQLMarker
abstract class Query(val name: String) : Element {
val children = arrayListOf<Element>()
protected fun <T : Element> visitEntity(entity: T, visit: T.() -> Unit = {}): T {
entity.visit()
children.add(entity)
return entity
}
override fun render(builder: StringBuilder, indent: String) {
builder.append("$indent$name")
if (children.isNotEmpty()) {
builder.append("{\n")
for (c in children) {
c.render(builder, "$indent ")
}
builder.append("$indent}")
}
builder.append("\n")
}
operator fun Query.unaryPlus() {
visitEntity(this,{})
}
override fun toString(): String {
val builder = StringBuilder()
render(builder, "")
return builder.toString()
}
}
Then I created the classes relevant to my case
class Filter private constructor(val filters: MutableMap<FilterType, Any>) {
class Builder {
private val filters = mutableMapOf<FilterType, Any>()
fun filters(key: FilterType, value: Any) = apply {
this.filters[key] = value
}
fun build(): Filter {
return Filter(filters)
}
}
}
class EVENTS(private val filter: Filter) : Query("events") {
override fun render(builder: StringBuilder, indent: String) {
builder.append("{$name")
if (filter.filters.isNotEmpty()) {
builder.append("(" + filter.filters.map {
if (it.value is Int || it.value is Long) {
it.key.str + ":" + it.value + ","
} else {
it.key.str + ":\"" + it.value + "\","
}
}.joinToString(" ").dropLast(1) + ")")
}
if (children.isNotEmpty()) {
builder.append("{\n")
for (c in children) {
c.render(builder, "$indent ")
}
builder.append("$indent}")
}
builder.append("\n}")
}
fun title() = visitEntity(TITLE())
fun genre() = visitEntity(GENRE())
fun image() = visitEntity(IMAGE())
fun link() = visitEntity(LINK())
fun other() = visitEntity(OTHER())
fun price() = visitEntity(PRICE())
fun text() = visitEntity(TEXT())
fun tickets() = visitEntity(TICKETS())
fun time() = visitEntity(TIME())
fun location(visit: LOCATION.() -> Unit) = visitEntity(LOCATION(), visit)
}
class TITLE : Query("title")
class GENRE : Query("genre")
class IMAGE : Query("image")
class LINK : Query("link")
class OTHER : Query("other")
class PRICE : Query("price")
class TEXT : Query("text")
class TICKETS : Query("tickets")
class TIME : Query("time")
class LOCATION : Query("location") {
fun area() = visitEntity(AREA())
fun place() = visitEntity(PLACE())
fun address(visit: ADDRESS.() -> Unit) = visitEntity(ADDRESS(), visit)
fun coordinates(visit: COORDINATES.() -> Unit) = visitEntity(COORDINATES(), visit)
}
class AREA : Query("area")
class PLACE : Query("place")
class ADDRESS : Query("address") {
fun city() = visitEntity(CITY())
fun street() = visitEntity(STREET())
fun no() = visitEntity(NO())
fun state() = visitEntity(STATE())
fun zip() = visitEntity(ZIP())
}
class CITY : Query("city")
class STREET : Query("street")
class NO : Query("no")
class STATE : Query("state")
class ZIP : Query("zip")
class COORDINATES : Query("coordinates") {
fun longitude() = visitEntity(LONGITUDE())
fun latitude() = visitEntity(LATITUDE())
}
class LONGITUDE : Query("longitude")
class LATITUDE : Query("latitude")
enum class FilterType(val str: String) {
PLACE("place"),
PRICELT("priceLT"),
PRICEGT("priceGT"),
TIMELT("timestampLT"),
TIMEGT("timestampGT"),
AREA("area"),
TITLE("title"),
GENRE("genre")
}
Some of the classes are edgecases and will not nest themself further down. So I was thinking if it is possible to simplify that a bit. And if I can use a unaryPlus to invoke them when I call them from the main() function, so I dont have to write {} after very single edgecase, when they dont have nesting anywaits
fun main(){
events(filter) {
title()
genre()
image()
link()
tickets()
other()
price()
text()
time()
location {
area()
place()
address {
city()
street()
no()
state()
zip()
}
coordinates {
longitude()
latitude()
}
}
}
}
Thank you in advance. Have a nice day!
回答1:
Yes, you can use unaryPlus for whatever you want
Check the Operator overloading documentation
Here you have a working example:
fun main() {
val events = events {
+title
+genre
}
println(events.render())
}
interface Element {
fun render() : String
}
@DslMarker //Domain Specific Language
annotation class GraphQLMarker
@GraphQLMarker
fun events(init: EventBody.() -> Unit): Element {
val events = EventBody()
events.init()
return events
}
class EventBody: Element {
override fun render() =
"events:${elements.joinToString { it.render() }}"
private val elements = mutableListOf<Element>()
operator fun Element.unaryPlus() = elements.add(this)
}
@GraphQLMarker
object title: Element {
override fun render() = "title"
}
@GraphQLMarker
object genre: Element {
override fun render() = "genre"
}
which outputs
events:title, genre
来源：https://stackoverflow.com/questions/65088556/is-it-possible-to-invoke-a-function-with-a-unaryplus-in-kotlin