Mark untrusted contracts

When interacting with external contracts, name your variables, methods, and contract interfaces in a way that makes it clear that interacting with them is potentially unsafe. This applies to your own functions that call external contracts.

// bad
Bank.withdraw(100); // Unclear whether trusted or untrusted

function makeWithdrawal(uint amount) { // Isn't clear that this function is potentially unsafe
    Bank.withdraw(amount);
}

// good
UntrustedBank.withdraw(100); // untrusted external call
TrustedBank.withdraw(100); // external but trusted bank contract maintained by XYZ Corp

function makeUntrustedWithdrawal(uint amount) {
    UntrustedBank.withdraw(amount);
}

Explicitly mark visibility in functions and state variables

Explicitly label the visibility of functions and state variables. Functions can be specified as being external, public, internal or private. Please understand the differences between them, for example external may be sufficient instead of public. For state variables, external is not possible. Labeling the visibility explicitly will make it easier to catch incorrect assumptions about who can call the function or access the variable.

// bad
uint x; // the default is private for state variables, but it should be made explicit
function buy() { // the default is public
    // public code
}

// good
uint private y;
function buy() external {
    // only callable externally
}

function utility() public {
    // callable externally, as well as internally: changing this code requires thinking about both cases.
}

function internalAction() internal {
    // internal code
}

Lock pragmas to specific compiler version

Contracts should be deployed with the same compiler version and flags that they have been tested the most with. Locking the pragma helps ensure that contracts do not accidentally get deployed using, for example, the latest compiler which may have higher risks of undiscovered bugs. Contracts may also be deployed by others and the pragma indicates the compiler version intended by the original authors.

// bad
pragma solidity ^0.4.4;


// good
pragma solidity 0.4.4;

Differentiate functions and events

Favor capitalization and a prefix in front of events (we suggest Log), to prevent the risk of confusion between functions and events. For functions, always start with a lowercase letter, except for the constructor.

// bad
event Transfer() {}
function transfer() {}

// good
event LogTransfer() {}
function transfer() external {}