21: Mapping

Mapping

Mapping is a data structure in Solidity that allows a programmer to store, retrieve and modify data in a key-value pair format. It is similar to a hash table or dictionary in other languages.

• Example 1 Let's assume we want to store a list of people and their ages. We can do this with a mapping like this:

mapping (address => uint) public peopleAges;

• Example 2 Now, let's assume we want to store a list of people and their names. We can do this with a mapping like this:

mapping (address => string) public peopleNames;

• Example 3 Finally, let's assume we want to store a list of people and their ages and names. We can do this with a mapping like this:

mapping (address => (uint, string)) public peopleAgesNames;

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Dynamic Mapping

Dynamic mapping is a data structure in Solidity that allows for variable keys and values. It is used to store data in a key-value format, as in a dictionary.

• Example 1 Consider the following example:

mapping(address => uint) public balances;

This creates a mapping from an address to a uint (unsigned integer). This means that each address in the blockchain can have its own integer value. This is useful for tracking balances or other values associated with each address.

• Example 2 Here is another example:

mapping(uint => string) public messages;

This creates a mapping from a uint (unsigned integer) to a string. This allows us to store a string value associated with a given integer. This could be used to track messages associated with a particular event or transaction.

• Example 3 Finally, here is an example using multiple data types:

mapping(address => mapping(uint => string)) public userData;

This creates a mapping from an address to a mapping of uints to strings. This allows us to store a string value associated with a given address and a given uint. This could be used to store user data associated with a particular address and a particular event or transaction.

That's it for the lesson 21! In the next lesson, Array