Kotlin versus java continued...

Along with Collections, the Kotlin standard library comes with sequences. Sequences are like iterables but they are not processed eagerly. Instead they are processed lazily when the result of the chain is required. Sequences perform all the operations on one item at a time while iterable completes each step for the collection and then proceeds to the next step. 

The Kotlin standard library offers two types of operations on collections – member functions and extension functions. Member functions define operations that are essential for a collection type. Implementations of collection interfaces must implement these member functions. Extension functions are for filtering, transforming, ordering and other collection processing functions. 

Transformations can be seen with examples involving mapping which applies a lambda function applied to each subsequent element. The order of results follows the order of elements. Zipping is another transformation which builds pairs with the elements from the same position in both collections. Extra elements in either collection beyond the common positions are ignored. Flat access to nested collections are also transformations. 

Kotlin is still behind C# in bringing SQL to language but Flink and Spark libraries make up for it. There is an ORM framework available natively for Kotlin called Exposed which has two layers of database access: typesafe SQL wrapping domain specific language and lightweight data access objects.