Repo structure

cadence/contracts/Recipe.cdc

@@ -1,10 +1,187 @@
+/// ExampleToken.cdc
+///
+/// The ExampleToken contract is a sample implementation of a fungible token on Flow.
+///
+/// Fungible tokens behave like everyday currencies -- they can be minted, transferred or
+/// traded for digital goods.
+///
+/// This is a basic implementation of a Fungible Token and is NOT meant to be used in production
+/// See the Flow Fungible Token standard for real examples: https://github.com/onflow/flow-ft
 
-import "FlowToken"
+access(all) contract ExampleToken {
+
+    access(all) entitlement Withdraw
+
+    access(all) let VaultStoragePath: StoragePath
+    access(all) let VaultPublicPath: PublicPath
+
+    access(all) var totalSupply: UFix64
+
+    /// Balance
+    ///
+    /// The interface that provides a standard field
+    /// for representing balance
+    ///
+    access(all) resource interface Balance {
+        access(all) var balance: UFix64
+    }
+
+    /// Provider
+    ///
+    /// The interface that enforces the requirements for withdrawing
+    /// tokens from the implementing type.
+    ///
+    /// It does not enforce requirements on `balance` here,
+    /// because it leaves open the possibility of creating custom providers
+    /// that do not necessarily need their own balance.
+    ///
+    access(all) resource interface Provider {
+
+        /// withdraw subtracts tokens from the implementing resource
+        /// and returns a Vault with the removed tokens.
+        ///
+        /// The function's access level is `access(Withdraw)`
+        /// So in order to access it, one would either need the object itself
+        /// or an entitled reference with `Withdraw`.
+        ///
+        /// @param amount the amount of tokens to withdraw from the resource
+        /// @return The Vault with the withdrawn tokens
+        ///
+        access(Withdraw) fun withdraw(amount: UFix64): @Vault {
+            post {
+                // `result` refers to the return value
+                result.balance == amount:
+                    "ExampleToken.Provider.withdraw: Cannot withdraw tokens!"
+                    .concat("The balance of the withdrawn tokens (").concat(result.balance.toString())
+                    .concat(") is not equal to the amount requested to be withdrawn (")
+                    .concat(amount.toString()).concat(")")
+            }
+        }
+    }
+
+    /// Receiver
+    ///
+    /// The interface that enforces the requirements for depositing
+    /// tokens into the implementing type.
+    ///
+    /// We do not include a condition that checks the balance because
+    /// we want to give users the ability to make custom receivers that
+    /// can do custom things with the tokens, like split them up and
+    /// send them to different places.
+    ///
+    access(all) resource interface Receiver {
+
+        /// deposit takes a Vault and deposits it into the implementing resource type
+        ///
+        /// @param from the Vault that contains the tokens to deposit
+        ///
+        access(all) fun deposit(from: @Vault)
+    }
+
+    /// Vault
+    ///
+    /// Each user stores an instance of only the Vault in their storage
+    /// The functions in the Vault are governed by the pre and post conditions
+    /// in the interfaces when they are called.
+    /// The checks happen at runtime whenever a function is called.
+    ///
+    /// Resources can only be created in the context of the contract that they
+    /// are defined in, so there is no way for a malicious user to create Vaults
+    /// out of thin air. A special Minter resource or constructor function needs to be defined to mint
+    /// new tokens.
+    ///
+    access(all) resource Vault: Balance, Provider, Receiver {
+
+		/// keeps track of the total balance of the account's tokens
+        access(all) var balance: UFix64
+
+        /// initialize the balance at resource creation time
+        init(balance: UFix64) {
+            self.balance = balance
+        }
+
+        /// withdraw
+        ///
+        /// Function that takes an integer amount as an argument
+        /// and withdraws that amount from the Vault.
+        ///
+        /// It creates a new temporary Vault that is used to hold
+        /// the money that is being transferred. It returns the newly
+        /// created Vault to the context that called so it can be deposited
+        /// elsewhere.
+        ///
+        access(Withdraw) fun withdraw(amount: UFix64): @Vault {
+            pre {
+                self.balance >= amount:
+                    "ExampleToken.Vault.withdraw: Cannot withdraw tokens! "
+                    .concat("The amount requested to be withdrawn (").concat(amount.toString())
+                    .concat(") is greater than the balance of the Vault (")
+                    .concat(self.balance.toString()).concat(").")
+            }
+            self.balance = self.balance - amount
+            return <-create Vault(balance: amount)
+        }
+
+        /// deposit
+        ///
+        /// Function that takes a Vault object as an argument and adds
+        /// its balance to the balance of the owners Vault.
+        ///
+        /// It is allowed to destroy the sent Vault because the Vault
+        /// was a temporary holder of the tokens. The Vault's balance has
+        /// been consumed and therefore can be destroyed.
+        access(all) fun deposit(from: @Vault) {
+            self.balance = self.balance + from.balance
+            destroy from
+        }
+    }
+
+    /// createEmptyVault
+    ///
+    access(all) fun createEmptyVault(): @Vault {
+        return <-create Vault(balance: 0.0)
+    }
+
+	// VaultMinter
+    //
+    // Resource object that an admin can control to mint new tokens
+    access(all) resource VaultMinter {
+
+		// Function that mints new tokens and deposits into an account's vault
+		// using their `{Receiver}` reference.
+        // We say `&{Receiver}` to say that the recipient can be any resource
+        // as long as it implements the Receiver interface
+        access(all) fun mintTokens(amount: UFix64, recipient: Capability<&{Receiver}>) {
+            let recipientRef = recipient.borrow()
+            ?? panic("ExampleToken.VaultMinter.mintTokens: Could not borrow a receiver reference to "
+                     .concat("the specified recipient's ExampleToken.Vault")
+                     .concat(". Make sure the account has set up its account ")
+                     .concat("with an ExampleToken Vault and valid capability."))
+
+            ExampleToken.totalSupply = ExampleToken.totalSupply + UFix64(amount)
+            recipientRef.deposit(from: <-create Vault(balance: amount))
+        }
+    }
+
+    /// The init function for the contract. All fields in the contract must
+    /// be initialized at deployment. This is just an example of what
+    /// an implementation could do in the init function. The numbers are arbitrary.
+    init() {
+        self.VaultStoragePath = /storage/CadenceFungibleTokenTutorialVault
+        self.VaultPublicPath = /public/CadenceFungibleTokenTutorialReceiver
+
+        self.totalSupply = 30.0
+
+        // create the Vault with the initial balance and put it in storage
+        // account.save saves an object to the specified `to` path
+        // The path is a literal path that consists of a domain and identifier
+        // The domain must be `storage`, `private`, or `public`
+        // the identifier can be any name
+        let vault <- create Vault(balance: self.totalSupply)
+        self.account.storage.save(<-vault, to: self.VaultStoragePath)
+
+        // Create a new VaultMinter resource and store it in account storage
+        self.account.storage.save(<-create VaultMinter(), to: /storage/CadenceFungibleTokenTutorialMinter)
 
-access(all) contract Recipe {
-    // Creating an empty vault
-    access(all)
-    fun createEmptyVault(): @FlowToken.Vault {
-        return <-create FlowToken.Vault(balance: 0.0)
     }
 }