My URL in Kotlin has an extra & at the end of it - dictionary

Question

private val BASE_URL = "https://itunes.apple.com/search?"
private var iTunesMap = mutableMapOf("term" to "parameter1",
"media" to "parameter2")
fun URL.addParameters(map:Map<String,String>) : String {
var newURL = BASE_URL
for(parameter in iTunesMap.iterator())
{
newURL += parameter.key + "=" + parameter.value + "&"
}
return newURL
}
I am ending up with a & at the end of the URL.
How do I prevent this from happening?

Answer 1

You can simply do it in a functional way:
val parameters = map.map { (key, value) -> // 1
"$key=$value" // 2
}.joinToString("&") // 3
return BASE_URL + parameters // 4
Explenation:
We use map function with destructuring declaration of parameters (key, value) which correspond to key and value in each map entry
For each map entry we create string key=value ($ is indicator, that we want to use value of some variable - in that case we use value of parameter key and parameter value
After .map function we have collection of strings: term=parameter1 and media=parameter2, we are joining them with & separator
Lastly we need to concatenate parameters to base url
If I can suggest - I would make this function more general by putting baseUrl as parameter - then you can use the same function for different urls.
EDIT
As Михаил Нафталь suggested in his answer, you can add prefix to joinToString function so you don't have to concatenate parameters with base url. So after that improvement your code will look like this:
return map.map { (key, value) ->
"$key=$value"
}.joinToString("&", prefix = BASE_URL )
Or you can do all of this using just joinToString function with giving transform function. (look for Михаил Нафталь answer)

Answer 2

Here is a one-liner:
map.entries.joinToString(separator = "&", prefix = BASE_URL) { (key, value) -> "$key=$value" }

Answer 3

Strings are immutable and += involves copying the entire string into a new string. Do not use += on a var: String in a loop, as that is O(N²); use a StringBuilder instead.
val urlBuilder = StringBuilder(BASE_URL)
iTunesMap.entries.joinTo(urlBuilder, separator = "&") { (key, value) ->
"$key=$value"
}
return urlBuilder.toString()