Mastering Blockchain Programming with Solidity

Iterable map pattern

The iterable map pattern allows you to iterate over the mapping entries. 

In Solidity, you can define a mapping. The mapping holds the key-value pairs. However, there is no way to iterate over the mapping entries in Solidity. There are some cases for which you would need to iterate over the mapping entries; for these situations, you can use this pattern.

Note that the iteration over the mapping entries should not cause an out-of-gas exception. To avoid these situations, use the iteration only in the view function. This way, you would execute a function via message calls only, without generating a transaction.

In the following code, we have DepositContract, in which anyone can deposit ether. When ether is deposited, its ...