Assigning Values to an Array

Assigning Values to an Array was a programming task. It has been deprecated for reasons that are discussed in its talk page.

Please do not add new code, and move existing code to the Arrays task.

In this task, the goal is to assign a value to an element of an array. The value should only replace an existing value, and not insert a new key should the key not exist. If the key does not exist, an error should be returned.