What is typed array in kotlin

Arrays are generic data structures because they can contain different types of elements. You can have Array<Int> or Array<String> for instance.

There is no separate concept of "typed" array. The reason for the name of toTypedArray is (I guess) to distiguish it from toArray() which returns an Array<Any?> (without useful type information about its elements, because everything is a Any? in Kotlin).

The reason why those 2 exist is because arrays on the JVM cannot be created without knowing the element type. This means that, in general, you cannot create an arbitrary array generically because generics are erased at runtime so you wouldn't actually know the correct element type at that time. This is why the simple toArray method either returns Array<Any?> or takes an extra array argument. The extra argument allows to either avoid creating the destination array, or at least provides sufficient type information at runtime to create an array of the same type.

In Kotlin, we can go one step further and actually use reified types to use information that we have at compile time to generate more specific code, such as code that create an array of a specific type (not generically, but still with the correct element type). This is what toTypedArray does by reifying its type parameter.