Many minor updates

solidity.html.markdown

@@ -14,7 +14,7 @@ As Solidity and Ethereum are under active development, experimental or beta feat
 ```javascript
 // Let's start with a simple Bank contract, before diving into to the key components of the language
 
-// START EXAMPLE
+// ** START EXAMPLE **
 // Start with a Natspec comment (the three slashes) that can be used
 // for documentation - and as descriptive data for UI elements
 /// @title A simple deposit/withdrawal bank built on Bitcoin
@@ -29,8 +29,7 @@ contract AcmeBank {
     mapping (address => uint) balances;
 
     // the 'public' makes 'owner' externally readable by users or contracts
-    // (but not writeable), the 'constant' means this value to be 
+    // (but not writeable) -
-    // changed after initialization
     address public owner;
 
     // Constructor, can receive one or many variables here
@@ -40,13 +39,13 @@ contract AcmeBank {
       owner = msg.sender; // msg.sender refers to the address of the contract creator
     }
 
-    function deposit(uint balance) {
+    function deposit(uint balance) public {
         balances[msg.sender] += msg.value; // no need for "this." or "self." in front of the state variable
 
         return balances[msg.sender]; // msg.sender refers to the contract caller
     }
 
-    function withdraw(uint withdrawAmount) returns (uint remainingBalance) {
+    function withdraw(uint withdrawAmount) public returns (uint remainingBalance) {
       if(balances[msg.sender] >= withdrawAmount) {
         balances[msg.sender] -= withdrawAmount;
 
@@ -58,7 +57,8 @@ contract AcmeBank {
       }
     }
 
-    // It's good practice to have a remove function, which disables this contract - but does mean that users have to trust the owner
+    // It's good practice to have a remove function, which disables this
+    // contract - but does mean that users have to trust the owner
     function remove() {
       if(msg.sender == owner) { // Only let the contract creator do this
         suicide(owner); // suicide makes this contract inactive, and returns funds to the owner
@@ -71,29 +71,35 @@ contract AcmeBank {
     }
 
     // Fallback function
-    // This function is called if invalid data is sent or ether without data; 
+    // The fallback function is called if none of the other functions matches the given function identifier.
+    // It is often meant to be called when invalid data is sent or ether without data.
     // Added so that ether sent to this contract is reverted if the contract fails
     // otherwise, the sender loses their money; you should add this in most contracts
     function () { throw; }
 }
-// END EXAMPLE
+// ** END EXAMPLE **
 
 // Now let's go through the basics of Solidity
 
-// 1. DATA TYPES
+// 1. DATA TYPES AND ASSOCIATED METHOD
 // uint is the data type typically used for currency (there are no doubles
 //  or floats) and for dates
 uint x;
-int constant a = 8; // int of 256 bits, cannot be changed after instantiation
+
+
+// with 'constant', the compiler replaces each occurence with the acutal value
+// int of 256 bits, cannot be changed after instantiation
+int constant a = 8;
+int256 constant a = 8; // same effect as line above, here the 256 is explict
+
+// For both int and uint, you can explicitly set space in steps of 8
+// e.g., int8, int16
 uint8 b;
 int64 c;
-// int256 is same as int
-// For both int and uint, you can explicitly set space in steps of 8, 
-// e.g., int8, int16
 uint248 e;
 
 // Type casting
-int x = int(b)
+int x = int(b);
 
 bool b = true; // or do 'var b = true;' for inferred typing
 
@@ -123,13 +129,14 @@ var a = true;
 
 // by default, all values are set to 0 on instantiation
 
-// Delete can be called on most types, and will set the values to 0
+// Delete can be called on most types, and will set the values to 0 by assignment
 uint x = 5;
 delete(x); // x is now 0
 
 // 2. DATA STRUCTURES
 // Arrays
-bytes32[] names;
+bytes32[5] nicknames; // static array
+bytes32[] names; // dynamic array
 uint newLength = names.push("John"); // adding returns new length of the array
 // Length
 names.length; // get length
@@ -168,29 +175,39 @@ delete(b); // set all values to 0, except any mappings
 enum State { Created, Locked, Inactive };
 State public state; // Declare variable from enum
 state = State.Created;
+// enums can be explicitly converted to ints
+
+// Data locations: Memory vs. storage - all complex types (arrays, structs) have a data location
+// 'memory' does not persist, 'storage' does
+// Default is 'storage' for local and state variables; 'memory' for function parameters
 
 // 3. Variables of note
-// storage - A persistent storage hash (does not need to be declared)
+// ** this **
-storage['abc'] = 'def'; // maps 256 bit words to 256 bit words
+this; // the address of the current contract
+// 'balance' often used at the end of a contracts life to send the
+// remaining balance to a party
+this.balance;
+this.someFunction(); // calls a function externally (via a message call, not via an internal jump)
 
-// tx - This transaction
+// ** msg - The current message received by the contract ** **
-tx.origin // address, sender of the transaction
-tx.gasprice // uint, gas price of the transaction
-
-// msg - The current message received by the contract
 msg.sender; // address, The address of the sender
 msg.value; // uint, The amount of gas provided to this contract in wei
-msg.data // bytes, complete call data
+msg.data; // bytes, complete call data
+msg.gas; // remaining gas
 
-// balance of the current contract (both contract and external accounts 
+// ** tx - This transaction **
-// have balances) - often used at the end of a contracts life to send the 
+tx.origin; // address, sender of the transaction
-// remaining balance to a party
+tx.gasprice; // uint, gas price of the transaction
-this.balance 
+
-// block
+// ** block - Information about the current block **
 now // uint, current time, alias for block.timestamp
-block.number // uint, current block number
+block.number; // uint, current block number
-block.difficulty // uint, current block difficulty
+block.difficulty; // uint, current block difficulty
-block.blockhash(1) // returns bytes32, only provides for most recent 256 block
+block.blockhash(1); // returns bytes32, only provides for most recent 256 blocks
+block.gasLimit();
+
+// ** storage - A persistent storage hash (does not need to be declared) **
+storage['abc'] = 'def'; // maps 256 bit words to 256 bit words
 
 // 4. FUNCTIONS AND MORE
 // A. Functions
@@ -236,7 +253,7 @@ function b() {
 
 // B. Events
 // Events are an easy way to notify external listeners that something changed
-// You typically decalre them after your contract parameters
+// You typically declare them after your contract parameters
 event Sent(address from, address to, uint amount);
 
 // You then call it in a function, when you want to trigger it
@@ -259,37 +276,49 @@ Coin.Sent().watch({}, '', function(error, result) {
 // contract)
 
 // C. Modifiers
-// Modifiers let you validate inputs to functions
+// Modifiers let you validate inputs to functions such as a minimal balance or user authentication
-// The '_' (underscore) must be included, and is an indicator that the 
+// It's similar to a guard clause in other languages
+
+// The '_' (underscore) must be included as the last line in the function body, and is an indicator that the
 // function being called should be placed there
 modifier onlyBefore(uint _time) { if (now >= _time) throw; _ }
 
 // You can then append it right after the function declaration
-function test()
+function changeOwner(newOwner)
-  onlyBefore()
+  onlyBefore(someTime)
   {
-
+  owner = newOwner;
 }
 
 // 5. BRANCHING AND LOOPS
 
 // All basic logic blocks work - including if/else, for, while, break, continue, return
 // switch is not provided
+
 // Syntax is the same as javascript, but there is no type conversion from
-// non-boolean to boolean
+// non-boolean to boolean, so comparison operators must be used to get the boolean value
 
-// 6. CALLING AN EXTERNAL CONTRACT
+// 6. OBJECTS/CONTRACTS
 
+// A. Calling an external contract
 contract infoFeed {
   function info() returns (uint ret) { return 42; }
 }
 
 contract Consumer {
   InfoFeed feed; // create a variable that will point to a contract on the blockchain
+
+  // Set feed to an existing contract
   function setFeed(address addr) {
     // Link to the contract by creating on the address
     feed = InfoFeed(addr);
   }
+
+  // Set feed based to a new instance of the contract
+  function createNewFeed() {
+    feed = new InfoFeed();
+  }
+
   function callFeed() {
     // T final parentheses call the contract, optionally adding
     // custom value or gas numbers
@@ -297,6 +326,30 @@ contract Consumer {
   }
 }
 
+// B. Inheritance
+
+// Order matters, last inherited contract (i.e., 'def') can override parts of the previously
+// inherited contracts
+contact MyContract is abc, def("a custom argument to def") {
+
+// Override function
+
+  function z() {
+    if (msg.sender == owner) {
+      def.z(); // call overridden function
+    }
+  }
+
+  };
+
+// C. Import
+
+import "filename";
+import "github.com/ethereum/dapp-bin/library/iterable_mapping.sol";
+
+// Importing is under active development and will change
+// Importing cannot currently be done at the command line
+
 // 7. CONTRACT DESIGN PATTERNS
 
 // A. Obfuscation
@@ -317,6 +370,13 @@ if (!addr.send(123)) {
 // Suicide
 suicide(SOME_ADDRESS); // suicide the current contract, sending funds to the address (often the creator)
 
+// This is a common pattern that lets the owner end the contract
+function remove() {
+  if(msg.sender == owner) { // Only let the contract creator do this
+    suicide(owner); // suicide makes this contract inactive, and returns funds to the owner
+  }
+}
+
 // D. Storage optimization
 // Reading and writing can be expensive, as data needs to be stored in the
 // blockchain forever - this encourages smart ways to use memory (eventually,
@@ -324,19 +384,20 @@ suicide(SOME_ADDRESS); // suicide the current contract, sending funds to the add
 // planning your data structures)
 
 // *** EXAMPLE: Let's do a more complex example ***
+
+// ** START EXAMPLE **
 // [TODO: Decide what a more complex example looks like, needs a few characteristics:
 //   - has a 'constant' state variable
-//   - has a state machine (uses modifier)
+//   - has a state machine (and uses modifier)
 //   - sends money to an address
 //   - gets information from another contract (we'll show code for both contracts)
 //   - Shows inheritance
 //   - show variables being passed in on instantiation (and guard code to throw if variables not provided)
-//   - Shows the swapping out of a contract
+//   - Shows the swapping out of a contract address
 //   Ideas:
 //     - crowdfunding?
 //     - Peer to peer insurance
 // ]
-
 // *** END EXAMPLE ***
 
 // Some final points
@@ -366,21 +427,21 @@ sha3("ab", "cd");
 ripemd160("abc");
 sha256("def");
 
-// These are natspec comments, when a user is asked to confirm a transaction
+// 8. COMMON MISTAKES/MISCONCEPTIONS
-/// 
+// A few common mistakes and misconceptions:
-/** */
 
-// 8. COMMON MISTAKES
+// A. You cannot restrict a human or computer from reading the content of
-// A few common mistakes
-// You cannot restrict a human or computer from reading the content of 
 // your transaction or a transaction's state
 
 // All data to the start of time is stored in the blockchain, so you and
-// anyone can observe all previous data states
+// anyone can observe all previous data stats
 
-// 9. TESTING
+// When you don't specify public on a variable, you are indicating that other *contracts* can't
+// read the data - but any person can still read the data
 
-// 10. STYLE NOTES
+// TODO
+
+// 9. STYLE NOTES
 // Use 4 spaces for indentation
 // (Python's PEP8 is used as the baseline style guide, including its general philosophy)
 ```
@@ -391,4 +452,7 @@ sha256("def");
 - [Browser-based Solidity Editor](http://chriseth.github.io/browser-solidity/)
 - [Gitter Chat room](https://gitter.im/ethereum/go-ethereum)
 
+## Information purposefully excluded
+- Libraries
+
 Feel free to send a pull request with any edits - or email nemild -/at-/ gmail