The code below is creating a new map called nameTable, then adding an entry named example to it, then trying to print the name property of the Value.
When I run it, it seems that the plus operation didn't add a new entry to the map like I thought it would.
So what am I doing wrong?
class Person(name1: String, lastName1: String, age1: Int){
var name: String = name1
var lastName: String = lastName1
var age: Int = age1
}
var nameTable: MutableMap<String, Person> = mutableMapOf()
var example = Person("Josh", "Cohen", 24)
fun main (args: Array<String>){
nameTable.plus(Pair("person1", example))
for(entry in nameTable){
println(entry.value.age)
}
}
While we're at it, I would love some examples of how to add, remove, and get an entry from a map.
Answer
The reason for your confusion is that plus is not a mutating operator, meaning that it works on (read-only) Map, but does not change the instance itself. This is the signature:
operator fun <K, V> Map<out K, V>.plus(pair: Pair<K, V>): Map<K, V>
What you want is a mutating operator set, defined on MutableMap:
operator fun <K, V> MutableMap<K, V>.set(key: K, value: V)
So your code may be rewritten (with some additional enhancements):
class Person(var name: String, var lastName: String, var age: Int)
val nameTable = mutableMapOf<String, Person>()
val example = Person("Josh", "Cohen", 24)
fun main (args: Array<String>) {
nameTable["person1"] = example
for((key, value) in nameTable){
println(value.age)
}
}