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Several fixes per Andreas's feedback
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@ -14,28 +14,30 @@ As Solidity and Ethereum are under active development, experimental or beta feat
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```javascript
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// Let's start with a simple Bank contract, before diving into to the key components of the language
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// START EXAMPLE
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// Start with a Natspec comment (the three slashes) that can be used
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// for documentation - and as descriptive data for UI elements
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/// @title A simple deposit/withdrawal bank built on Bitcoin
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// All contracts are declared and named (in CamelCase)
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// They are similar to 'class' in other languages (and allow capabilities like inheritance)
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contract AcmeBank {
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// Declare state variables outside a function,
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// these are persistent throughout the life of the contract
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// a dictionary that maps addresses to balances
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mapping (address -> uint) balances;
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mapping (address => uint) balances;
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// the 'public' makes 'owner' externally readable by users or contracts
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// (but not writeable), the 'constant' means this value to be
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// changed after initialization
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address public constant owner;
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address public owner;
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// Constructor, can receive one or many variables here
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function AcmeBank() {
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// msg is a default variable that provides both the
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// contract messager's address and amount
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owner = msg.address; // msg.address refers to the address of the contract creator
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owner = msg.sender; // msg.sender refers to the address of the contract creator
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}
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function deposit(uint balance) {
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@ -48,7 +50,7 @@ contract AcmeBank {
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if(balances[msg.sender] >= withdrawAmount) {
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balances[msg.sender] -= withdrawAmount;
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if (!balances[msg.sender].send(withdrawAmount)) {
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if (!msg.sender.send(withdrawAmount)) {
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balances[msg.sender] += withdrawAmount;
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}
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@ -56,7 +58,7 @@ contract AcmeBank {
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}
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}
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// It's good practice to have a remove function, which disables this contract
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// It's good practice to have a remove function, which disables this contract - but does mean that users have to trust the owner
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function remove () {
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if(msg.sender == owner) { // Only let the contract creator do this
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suicide(owner); // suicide makes this contract inactive, and returns funds to the owner
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@ -74,7 +76,7 @@ contract AcmeBank {
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// otherwise, the sender loses their money; you should add this in most contracts
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function () { throw; }
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}
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// End example
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// END EXAMPLE
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// Now let's go through the basics of Solidity
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@ -82,7 +84,7 @@ contract AcmeBank {
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// uint is the data type typically used for currency (there are no doubles
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// or floats) and for dates
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uint x;
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int const a = 8; // int of 256 bits, cannot be changed after instantiation
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int constant a = 8; // int of 256 bits, cannot be changed after instantiation
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uint8 b;
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int64 c;
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// int256 is same as int
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@ -134,7 +136,7 @@ names.length; // get length
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names.length = 1; // lengths can also be set, unlike many other languages
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// Dictionaries (any type to any other type)
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mapping (string -> uint) public balances;
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mapping (string => uint) public balances;
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balances["john"] = 1;
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console.log(balances[jill]); // is 0, all non-set key values return zeroes
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// The 'public' lets you do the following from another contract
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@ -322,13 +324,14 @@ suicide(SOME_ADDRESS); // suicide the current contract, sending funds to the add
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// planning your data structures)
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// *** EXAMPLE: Let's do a more complex example ***
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// [TODO: Decide what a more complex example looks like, needs a few // characteristics:
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// [TODO: Decide what a more complex example looks like, needs a few characteristics:
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// - has a 'constant' state variable
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// - has a state machine (uses modifier)
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// - sends money to an address
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// - gets information from another contract (we'll show code for both contracts)
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// - Shows inheritance
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// - show variables being passed in on instantiation (and guard code to throw if variables not provided)
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// - Shows the swapping out of a contract
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// Ideas:
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// - crowdfunding?
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// - Peer to peer insurance
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@ -375,7 +378,9 @@ sha256("def");
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// All data to the start of time is stored in the blockchain, so you and
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// anyone can observe all previous data states
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// 9. STYLE NOTES
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// 9. TESTING
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// 10. STYLE NOTES
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// Use 4 spaces for indentation
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// (Python's PEP8 is used as the baseline style guide, including its general philosophy)
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```
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