feat: add ERC20 example (#100)

* feat: add ERC20 example

* fix: broken cairo format check quickfix

listings/ch01-applications/erc20/.gitignore

@@ -0,0 +1 @@
+target

listings/ch01-applications/erc20/Scarb.toml

@@ -0,0 +1,8 @@
+[package]
+name = "erc20"
+version = "0.1.0"
+
+[dependencies]
+starknet = ">=2.3.0-rc0"
+
+[[target.starknet-contract]]

listings/ch01-applications/erc20/src/lib.cairo

@@ -0,0 +1,4 @@
+mod token;
+
+#[cfg(test)]
+mod tests;

listings/ch01-applications/erc20/src/tests.cairo

@@ -0,0 +1,2 @@
+mod tests { // TODO
+}

listings/ch01-applications/erc20/src/token.cairo

@@ -0,0 +1,215 @@
+use starknet::ContractAddress;
+
+// ANCHOR: interface
+#[starknet::interface]
+trait IERC20<TContractState> {
+    fn get_name(self: @TContractState) -> felt252;
+    fn get_symbol(self: @TContractState) -> felt252;
+    fn get_decimals(self: @TContractState) -> u8;
+    fn get_total_supply(self: @TContractState) -> felt252;
+    fn balance_of(self: @TContractState, account: ContractAddress) -> felt252;
+    fn allowance(
+        self: @TContractState, owner: ContractAddress, spender: ContractAddress
+    ) -> felt252;
+    fn transfer(ref self: TContractState, recipient: ContractAddress, amount: felt252);
+    fn transfer_from(
+        ref self: TContractState,
+        sender: ContractAddress,
+        recipient: ContractAddress,
+        amount: felt252
+    );
+    fn approve(ref self: TContractState, spender: ContractAddress, amount: felt252);
+    fn increase_allowance(ref self: TContractState, spender: ContractAddress, added_value: felt252);
+    fn decrease_allowance(
+        ref self: TContractState, spender: ContractAddress, subtracted_value: felt252
+    );
+}
+// ANCHOR_END: interface
+
+// ANCHOR: erc20
+#[starknet::contract]
+mod erc20 {
+    use zeroable::Zeroable;
+    use starknet::get_caller_address;
+    use starknet::contract_address_const;
+    use starknet::ContractAddress;
+
+    #[storage]
+    struct Storage {
+        name: felt252,
+        symbol: felt252,
+        decimals: u8,
+        total_supply: felt252,
+        balances: LegacyMap::<ContractAddress, felt252>,
+        allowances: LegacyMap::<(ContractAddress, ContractAddress), felt252>,
+    }
+
+    #[event]
+    #[derive(Drop, starknet::Event)]
+    enum Event {
+        Transfer: Transfer,
+        Approval: Approval,
+    }
+    #[derive(Drop, starknet::Event)]
+    struct Transfer {
+        from: ContractAddress,
+        to: ContractAddress,
+        value: felt252,
+    }
+    #[derive(Drop, starknet::Event)]
+    struct Approval {
+        owner: ContractAddress,
+        spender: ContractAddress,
+        value: felt252,
+    }
+
+    mod Errors {
+        const APPROVE_FROM_ZERO: felt252 = 'ERC20: approve from 0';
+        const APPROVE_TO_ZERO: felt252 = 'ERC20: approve to 0';
+        const TRANSFER_FROM_ZERO: felt252 = 'ERC20: transfer from 0';
+        const TRANSFER_TO_ZERO: felt252 = 'ERC20: transfer to 0';
+        const BURN_FROM_ZERO: felt252 = 'ERC20: burn from 0';
+        const MINT_TO_ZERO: felt252 = 'ERC20: mint to 0';
+    }
+
+    #[constructor]
+    fn constructor(
+        ref self: ContractState,
+        recipient: ContractAddress,
+        name: felt252,
+        decimals: u8,
+        initial_supply: felt252,
+        symbol: felt252
+    ) {
+        self.name.write(name);
+        self.symbol.write(symbol);
+        self.decimals.write(decimals);
+        self.mint(recipient, initial_supply);
+    }
+
+    #[external(v0)]
+    impl IERC20Impl of super::IERC20<ContractState> {
+        fn get_name(self: @ContractState) -> felt252 {
+            self.name.read()
+        }
+
+        fn get_symbol(self: @ContractState) -> felt252 {
+            self.symbol.read()
+        }
+
+        fn get_decimals(self: @ContractState) -> u8 {
+            self.decimals.read()
+        }
+
+        fn get_total_supply(self: @ContractState) -> felt252 {
+            self.total_supply.read()
+        }
+
+        fn balance_of(self: @ContractState, account: ContractAddress) -> felt252 {
+            self.balances.read(account)
+        }
+
+        fn allowance(
+            self: @ContractState, owner: ContractAddress, spender: ContractAddress
+        ) -> felt252 {
+            self.allowances.read((owner, spender))
+        }
+
+        fn transfer(ref self: ContractState, recipient: ContractAddress, amount: felt252) {
+            let sender = get_caller_address();
+            self._transfer(sender, recipient, amount);
+        }
+
+        fn transfer_from(
+            ref self: ContractState,
+            sender: ContractAddress,
+            recipient: ContractAddress,
+            amount: felt252
+        ) {
+            let caller = get_caller_address();
+            self.spend_allowance(sender, caller, amount);
+            self._transfer(sender, recipient, amount);
+        }
+
+        fn approve(ref self: ContractState, spender: ContractAddress, amount: felt252) {
+            let caller = get_caller_address();
+            self.approve_helper(caller, spender, amount);
+        }
+
+        fn increase_allowance(
+            ref self: ContractState, spender: ContractAddress, added_value: felt252
+        ) {
+            let caller = get_caller_address();
+            self
+                .approve_helper(
+                    caller, spender, self.allowances.read((caller, spender)) + added_value
+                );
+        }
+
+        fn decrease_allowance(
+            ref self: ContractState, spender: ContractAddress, subtracted_value: felt252
+        ) {
+            let caller = get_caller_address();
+            self
+                .approve_helper(
+                    caller, spender, self.allowances.read((caller, spender)) - subtracted_value
+                );
+        }
+    }
+
+    #[generate_trait]
+    impl InternalImpl of InternalTrait {
+        fn _transfer(
+            ref self: ContractState,
+            sender: ContractAddress,
+            recipient: ContractAddress,
+            amount: felt252
+        ) {
+            assert(!sender.is_zero(), Errors::TRANSFER_FROM_ZERO);
+            assert(!recipient.is_zero(), Errors::TRANSFER_TO_ZERO);
+            self.balances.write(sender, self.balances.read(sender) - amount);
+            self.balances.write(recipient, self.balances.read(recipient) + amount);
+            self.emit(Transfer { from: sender, to: recipient, value: amount });
+        }
+
+        fn spend_allowance(
+            ref self: ContractState,
+            owner: ContractAddress,
+            spender: ContractAddress,
+            amount: felt252
+        ) {
+            let allowance = self.allowances.read((owner, spender));
+            self.allowances.write((owner, spender), allowance - amount);
+        }
+
+        fn approve_helper(
+            ref self: ContractState,
+            owner: ContractAddress,
+            spender: ContractAddress,
+            amount: felt252
+        ) {
+            assert(!spender.is_zero(), Errors::APPROVE_TO_ZERO);
+            self.allowances.write((owner, spender), amount);
+            self.emit(Approval { owner, spender, value: amount });
+        }
+
+        fn mint(ref self: ContractState, recipient: ContractAddress, amount: felt252) {
+            assert(!recipient.is_zero(), Errors::MINT_TO_ZERO);
+            let supply = self.total_supply.read() + amount; // What can go wrong here?
+            self.total_supply.write(supply);
+            let balance = self.balances.read(recipient) + amount;
+            self.balances.write(recipient, amount);
+            self
+                .emit(
+                    Event::Transfer(
+                        Transfer {
+                            from: contract_address_const::<0>(), to: recipient, value: amount
+                        }
+                    )
+                );
+        }
+    }
+}
+// ANCHOR_END: erc20
+
+

src/SUMMARY.md

@@ -25,6 +25,7 @@ Summary
 # Applications examples
   - [Upgradeable Contract](./ch01/upgradeable_contract.md)
   - [Defi Vault](./ch01/simple_vault.md)
+  - [ERC20 Token](./ch01/erc20.md)
 
 <!-- ch02 -->
 # Advanced concepts

src/ch01/erc20.md

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+# ERC20 Token
+
+Contracts that follow the [ERC20 Standard](https://eips.ethereum.org/EIPS/eip-20) are called ERC20 tokens. They are used to represent fungible assets.
+
+To create an ERC20 conctract, it must implement the following interface:
+
+```rust
+{{#include ../../listings/ch01-applications/erc20/src/token.cairo:interface}}
+```
+
+In Starknet, function names should be written in *snake_case*. This is not the case in Solidity, where function names are written in *camelCase*.
+The Starknet ERC20 interface is therefore slightly different from the Solidity ERC20 interface.
+
+Here's an implementation of the ERC20 interface in Cairo:
+
+```rust
+{{#include ../../listings/ch01-applications/erc20/src/token.cairo:erc20}}
+```
+
+Play with this contract in [Remix](https://remix.ethereum.org/?#activate=Starknet&url=https://github.com/NethermindEth/StarknetByExample/blob/main/listings/ch01-applications/erc20/src/token.cairo).
+
+There's several other implementations, such as the [Open Zeppelin](https://docs.openzeppelin.com/contracts-cairo/0.7.0/erc20) or the [Cairo By Example](https://cairo-by-example.com/examples/erc20/) ones.