day3.md

Chapter 3

Day 3

1. Define your own contract that stores a dictionary of resources. Add a function to get a reference to one of the resources in the dictionary.

pub contract Crypto {

    pub var dictionaryOfCoin: @{String: Coins}

    pub resource Coins {
        pub let token: String
        init(_token: String) {
            self.token = _token
        }
    }

    pub fun getReference(key: String): &Coins? {
        return &self.dictionaryOfCoin[key] as &Coins?
    }

    init() {
        self.dictionaryOfCoin <- {
            "Flow": <- create Coins(_token: "Coin "),
            "Dogecoin": <- create Coins(_token: "Shit Coin")
        }
    }
}

2. Create a script that reads information from that resource using the reference from the function you defined in part 1.

import Crypto from 0x01

pub fun main(): String {
  let ref = Crypto.coinsReference(key: "Flow") ?? panic("key not found")
  return ref.token
}

3. Explain, in your own words, why references can be useful in Cadence.

• We can use reference to get information without moving resource. It can also use with Struct.