working_with_structs.md

Chapter 7: Working With Structs and Mappings

Remember our Person struct in the previous example?

struct Person:
    age: uint256
    name: String[64]

people: HashMap[uint256, Person]

Now we're going to learn how to create new Persons and add them to our people mapping.

// create a New Person:
Person vasa = Person({ name: "vasa", age: 22 })

// Add that person to the mapping with key `0`:
self.people[0] = vasa

We can also combine these together and do them in one line of code to keep things clean:

self.people[0] = Person({ name: "vasa", age: 22 })

The self Variable

Notice that we are using self keyword to access the people (state) variable.

self is an environment variable used to reference a contract from within itself. self allows you to read and write to state variables and to call private (internal) functions within the contract. We will learn about external/internal functions in the next chapter.

self is used to access a contract’s state variables, as shown in the following example:

message: String[10]

@external
def setMessage(msg: String[10]):
    self.message = msg

self is also used to call internal functions within a contract:

@internal
def multiplyByTwo(amount: uint256):
    amount * 2

@external
def calculate(amount: uint256):
    self.multiplyByTwo(amount)

Put it to the test

Let's make our createPokemon function do something!

1. Remove the pass keyword. Fill in the function body so it creates a new Pokemon, and adds it to the pokemonList mapping. Use the following values for the new Pokemon:

   • name: name (from function argument),
   • dna: dna (from function argument),
   • HP: HP (from function argument),
   • matches: 0,
   • wins: 0

2. Do not forget to use the self environment variable to access pokemonList mapping.

3. Let's do it in one line of code to keep things clean.

** Template **

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** Solution **

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** Previous Chapter Solution **

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