Iterate through a set and print only one message instead of one for each item on set - kotlin

Question

I'm trying to iterate through a set to find an item. If the item is found, I want it to print a certain message and another message if item is not found. So far, it works but it print a message for each item on the set, whereas I only want one message to display: either if the item was found with the price or the message that it wasn't found. I understand this is happening because of the for loop but I'm not sure how to get it to display the not found message only once and iterate through the set all the same.
This is the code:
fun getArticleOut(code:String) {
fun onSuccess(price: Int): String {
return "Price is $price"
}
fun onError(): String {
return "Article not found"
}
for (i in house.articles) {
if (i.code.equals(code)) {
val price = calculatePrice(
articleType = i.articleType,
totalTime = i.totalTime.toInt(),
hasCard = !i.hasCard.isNullOrEmpty()
)
println(onSuccess(price))
house.articles.remove(i)
} else {
println(onError())
}
}
}
Just to clarify:
data class House(val articles: MutableSet<Articles>)
data class Articles(val code: String,
var articleType: ArticleType,
var totalTime: Calendar,
var hasCard:String?=" ")

Answer 1

The direct answer is the break statement, which breaks out of a for or while loop.  You'd then have to move the onError() call outside the loop, with some way of telling whether the loop completed or not.  For example:
var found = false
for (i in house.articles) {
if (i.code == code) {
val price = calculatePrice(
articleType = i.articleType,
totalTime = i.totalTime.toInt(),
hasCard = !i.hasCard.isNullOrEmpty())
println(onSuccess(price))
house.articles.remove(i)
found = true
break
}
}
if (!found)
println(onError())
If you don't need to do anything after both cases (as in the code in question), then you could simplify it to return, and avoid the flag:
for (i in house.articles) {
if (i.code == code) {
val price = calculatePrice(
articleType = i.articleType,
totalTime = i.totalTime.toInt(),
hasCard = !i.hasCard.isNullOrEmpty())
println(onSuccess(price))
house.articles.remove(i)
return
}
}
println(onError())
However, there are probably better approaches that don't need manual iteration.  Kotlin's standard library is so powerful that any time you find yourself writing a loop, you should stop and ask whether there's a library function that would make it simpler.
In particular, you could use find(), e.g.:
val article = house.articles.find{ it.code == code }
if (article != null) {
val price = calculatePrice(
articleType = article.articleType,
totalTime = article.totalTime.toInt(),
hasCard = !article.hasCard.isNullOrEmpty())
println(onSuccess(price))
house.articles.remove(article)
} else {
println(onError())
}
That makes the code easier to read, too.  (Note that the code is now saying what it's doing, not how it's doing it, which is usually an improvement.)
There are also deeper design questions worth asking, which could lead to further simplifications.  For example:
If code is a unique identifier for Article, another option would be to make articles a Map from code to the corresponding Article; both checking and removal would then be constant-time operations, so more efficient as well as more concise.  (Of course, that depends on how often you're doing these lookups, and what else is setting or using articles.)
Or you could override Article.equals() to check only the code.  Then you could create a dummy Article with the code you're looking for, and do a simple in test (which uses the set's contains method) to check for its presence.  Accessing and removing the ‘true’ one in the set would be harder, though, so that may not be a good fit.
Would be neater for calculatePrice() to be defined to take an Article directly?  (Obviously that depends on whether it could be calculating the price of anything else too.)  Could it even be a method or extension function on Article?  (That probably depends whether the price is conceptually a property of the article itself, or whether it's specific to the getArticleOut() function and any surrounding code.)
Also worth pointing out that the code in the question has a nasty bug (which all these changes also work around), which is that it's trying to modify a collection while iterating through it, which is dangerous!
If you're lucky, you'll get an immediate ConcurrentModificationException showing you exactly what went wrong; if you're less lucky it'll continue but do something unexpected, such as skipping over an element or giving an apparently-unrelated error later on…
Which is another reason to avoid manual iteration where possible.
(The only safe way to remove an element while iterating is to manage the Iterator yourself, and use that to do the removal.)