Interesting kotlin 0x06:list minus list

Recently http://portal.kotlin-academy.com/#/ I see a lot about Kotlin An interesting topic . I think it's very suitable for Kotlin lovers , If you are interested, you can check it by yourself .
【 amusing Kotlin 】 Record your understanding of each question in the series .

0x06：List minus list

fun main(args: Array<String>) {
    
    val list = listOf(1, 2, 3)
    print(list - 1)
    print(list - listOf(1))

    val ones = listOf(1, 1, 1)
    print(ones - 1)
    print(ones - listOf(1))
}

Above code , What is the result of the operation ？ optional ：

1. [2, 3][2, 3][1, 1][1, 1]
2. [2, 3][2, 3][1, 1][]
3. [2, 3][2, 3][][1, 1]
4. [2, 3][2, 3][][]

Think about it , Record the answers in your mind .

analysis

The title is as above , be familiar with Kotlin Set related operator logic friends should be able to get the answer soon , It's just about - One operator and two overloaded implementations .

The first overload implementation ：

The logic is to filter out the first and incoming parameters in the set element Equal elements .

The second overload implementation ：

Logic is to filter out all elements that are equal to any element in the second list .

The code in the question is equivalent to the following ：

fun main(args: Array<String>) {
    
    val list = listOf(1, 2, 3)
    print(list.minus(1))
    print(list.minus(listOf(1)))

    val ones = listOf(1, 1, 1)
    print(ones.minus(1))
    print(ones.minus(listOf(1)))
}

Look at the logic one by one

val list = listOf(1, 2, 3)
print(list - 1)           //  Filtering out the first equals  1  The elements of , The result is  [2, 3]
print(list - listOf(1))   //  Filter out everything that's equal to  1  The elements of , The result is  [2, 3]

val ones = listOf(1, 1, 1)
print(ones - 1)           //  Filtering out the first equals  1  The elements of , The result is  [2, 3]
print(ones - listOf(1))   //  Filter out everything that's equal to  1  The elements of , The result is  []

therefore , The correct answer is

Options 2 ：[2, 3][2, 3][1, 1][]

extend

Kotlin Use in operator Keywords are used to modify functions , Indicates that the function overloads an operator or implements a convention . Use operator Keyword modifies function and function name can only be component1、component2、component3 … When it comes to achieving an agreement , namely deconstruction .

By the way List Some other operators of （in 、+） as well as Deconstruction agreement .

fun main() {
    
    val list = listOf(1, 2, 3)
    println(2 in list)
    println(4 in list)
    println(list + 5)
    println(list + listOf(1, 2, 3))
    println(list + arrayOf(1, 2, 3))
    println(list + sequenceOf(1, 2, 3))

    val (v, w, x) = list
    println(v)
    println(w)
    println(x)
    
    println(list.component1())
    println(list.component2())
    println(list.component3())
    println(list.component4())
    println(list.component5())

}

The operation results are as follows ：

componentN Up to 5, And receiver by List<T>, The internal call is actually get() function , So when the index exceeds the length of the list , Run time error .

in the light of operator and componentN It's the way we work together , For example ：

class Location(val x: Int, val y: Int) {
    
    operator fun component1() = x
    operator fun component2() = y
}

fun main() {
    
    val location = Location(520, 1314)
    val (x, y) = location

    println(x)
    println(y)
}

Running results ：

For operator overloading , For example ：

operator fun Location.minus(location: Location): Location {
    
    return Location(this.x - location.x, this.y - location.y)
}

operator fun Location.plus(location: Location): Location {
    
    return Location(this.x + location.x, this.y + location.y)
}

operator fun Location.contains(location: Location): Boolean {
    
    return this.x > location.x && this.y > location.y
}


class Location(val x: Int, val y: Int) {
    
    operator fun component1() = x
    operator fun component2() = y

    override operator fun equals(other: Any?): Boolean =
        other is Location && this.x == other.x && this.y == other.y

    override fun hashCode(): Int {
    
        var result = x
        result = 31 * result + y
        return result
    }

    override fun toString(): String {
    
        return "($x, $y)"
    }
}

fun main() {
    
    val location = Location(520, 1314)
    val (x, y) = location

    println(x)
    println(y)

    val other = Location(1, 2)
    println(location - other)
    println(location + other)
    println(location == other)
    println(other in location)
}

The operation results are as follows ：

Pay attention to the ：equals Operator overloading can only be implemented as a class member function , Because this function is already in Any Definition in class .

In the process of writing , Android Studio Will give us friendly tips , Not the kui is a YYDS .

summary

• operators overloading
• deconstruction