A fixed-supply token with transfers and allowance spending, deployed March 2016.
Historical Significance
Instead of decrementing an allowance as it is drawn, this revision of the tutorial keeps a separate ledger of how much of each approval has been spent and compares against it. The result is the same limit enforced from the opposite direction, and it avoids the write-after-read that made the ERC-20 approve race famous. It is a road the standard did not take, preserved in the contracts that copied the tutorial while it was still there.
Context
Ethereum's Frontier network went live on 30 July 2015. Contracts were compiled and deployed from the geth console, there was no test network in common use, and the material people copied from was the ethereum.org tutorials, the Solidity documentation and the go-ethereum wiki. Almost everything deployed in these months is somebody trying the tools.
Token Information
Key Facts
Description
A token from the ethereum.org tutorial. Balances sit in a public balanceOf mapping and transfer(to, value) moves them, throwing rather than returning false when the sender is short and checking the recipient's balance for overflow before adding to it. An allowance mapping records what each spender has been authorised for. ApproveAndCall sets the allowance and calls receiveApproval on the spender in the same transaction, so a spending contract learns of its allowance at the moment it is granted. A separate spentAllowance ledger records how much of each approval has already been drawn, rather than decrementing the allowance itself. There is no owner and no way to create further units: the supply written at deployment is the whole supply. It was deployed as WarBits, with the symbol // and 8 decimal places.
Source Verified
Historian Categories
Heuristic Analysis
The following characteristics were detected through bytecode analysis and may not be accurate.
Frontier Era
The initial release of Ethereum. A bare-bones implementation for technical users.
Bytecode Overview
Verified Source Available
Source verified through compiler archaeology and exact bytecode matching.
View Verification ProofShow source code (Solidity)
// Submitted by EthereumHistory (ethereumhistory.com)
contract tokenRecipient { function receiveApproval(address _from, uint256 _value, address _token, bytes _extraData); }
contract MyToken {
/* Public variables of the token */
string public name;
string public symbol;
uint8 public decimals;
mapping (address => uint256) public balanceOf;
mapping (address => mapping (address => uint256)) public allowance;
mapping (address => mapping (address => uint256)) public spentAllowance;
/* This generates a public event on the blockchain that will notify clients */
event Transfer(address indexed from, address indexed to, uint256 value);
/* Initializes contract with initial supply tokens to the creator of the contract */
function MyToken(uint256 initialSupply, string tokenName, uint8 decimalUnits, string tokenSymbol) {
balanceOf[msg.sender] = initialSupply; // Give the creator all initial tokens
name = tokenName; // Set the name for display purposes
symbol = tokenSymbol; // Set the symbol for display purposes
decimals = decimalUnits; // Amount of decimals for display purposes
}
/* Send coins */
function transfer(address _to, uint256 _value) {
if (balanceOf[msg.sender] < _value) throw; // Check if the sender has enough
if (balanceOf[_to] + _value < balanceOf[_to]) throw; // Check for overflows
balanceOf[msg.sender] -= _value; // Subtract from the sender
balanceOf[_to] += _value; // Add the same to the recipient
Transfer(msg.sender, _to, _value); // Notify anyone listening that this transfer took place
}
/* Allow another contract to spend some tokens in your behalf */
function approveAndCall(address _spender, uint256 _value, bytes _extraData) returns (bool success) {
allowance[msg.sender][_spender] = _value;
tokenRecipient spender = tokenRecipient(_spender);
spender.receiveApproval(msg.sender, _value, this, _extraData);
}
/* A contract attempts to get the coins */
function transferFrom(address _from, address _to, uint256 _value) returns (bool success) {
if (balanceOf[_from] < _value) throw; // Check if the sender has enough
if (balanceOf[_to] + _value < balanceOf[_to]) throw; // Check for overflows
if (spentAllowance[_from][msg.sender] + _value > allowance[_from][msg.sender]) throw; // Check allowance
balanceOf[_from] -= _value; // Subtract from the sender
balanceOf[_to] += _value; // Add the same to the recipient
spentAllowance[_from][msg.sender] += _value;
Transfer(msg.sender, _to, _value); // Notify anyone listening that this transfer took place
}
/* This unnamed function is called whenever someone tries to send ether to it */
function () {
throw; // Prevents accidental sending of ether
}
}External Links
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