Mastering Blockchain Programming with Solidity

Indexed map pattern

The indexed map pattern allows you to read an entry from a map using an index. The pattern also allows you to remove an item from a map and an array.

As we have seen in the previous section, in an iterable map pattern, an item is added to a map as well as to an array. Using the iterable map, we can fetch records using an index. However, the iterable map pattern is useful when you just want to keep on adding items in a map and in an array; it does not support the removal of an item. Hence, when you want to remove an item from the map and array, things get a little tricky. Here, in the IndexedMapping library contract, we can maintain the list of items and remove them from the list as well:

library IndexedMapping {    struct ...