For-in loop
It's cumbersome to write a for loop and manually decide the end condition.
If you want to iterate over a collection, you can use the for .. in ... {} loop.
In the first for-in loop, we iterate over an array. The loop will bind each
element to the variable element in each iteration.
We can also iterate over a map with key-value pairs. The second loop will bind
the key to the first variable (k) and the value to the second variable (v).
Which collections can be iterated over with a for-in loop? And when does the for-in loop support two variables? The for-in loop functionality actually depends on the API of the collection:
-
If the collection provides an
iter()method to return anIter[V]iterator, then the for-in loop can iterate over it with a single variable. -
If the collection provides an
iter2()method to return anIter2[K,V]iterator, you can use two variables to iterate over it.
We will explain more details about the iterator in a later chapter.
fn main {
println("\nfor-in loop:")
let array = [1, 2, 3]
for element in array {
println("element: \{element}")
}
println("\nfor-in loop for map:")
let map = { "key1": 1, "key2": 2, "key3": 3 }
for k, v in map {
println("key: \{k}, value: \{v}")
}
}