$174.63 1.65%
ETH · 84w

How to write clean, elegant Solidity code using function modifiers — Colony

How to write clean, elegant Solidity code using function modifiers

One of the most interesting features in Solidity are function modifiers. When added to a function body they extend it, allowing us to abstract parts of our code and write functions with fewer conditionals checks intertwined with state changes.

Creating a function modifier

The syntax looks similar to declaring a function, except it uses the modifier keyword. The underscore on indicates how the original function is changed:

modifier assertValueIsOne(uint value) { assert(value == 1); _; // original function goes at this point} function doSomething(uint value) assertValueIsOne(value){ } Use cases

Checking for invariants or conditions using require, revert (throw is deprecated, see more here) or assert accordingly:

// For parameterless modifiers, we can omit parenthesismodifier isAllowed { assert(msg.sender == owner); // contract state _;} modifier isValidAddress(address target) { require(target != 0x0); _;} modifier isValueBiggerThanZero(uint value) { require(value > 0); _;} function isOwner(address target) constant returns (bool) { return target == owner;} function simpleFunction(address target) isValidAddress(target) isValueBiggerThanZero(msg.value) isAllowed // omitted parenthesis for parameterless modifiers payable{ // do something} Please note that modifiers are applied to the original function in the order they are presented on the function declaration, i.e: isValidAddress, isValueBiggerThanZero, isAllowed and then payable.

Checking for msg.sender permissions:

modifier isOwner { assert(owner == msg.sender); _;} function finalize() isOwner { finalized = true;}

Raising events before or after a function is called:

event StartEvent();event FinishEvent(); modifier logEvents { StartEvent(); _; FinishEvent();} function toggle () logEvents { } Conclusion

Before formal verification or code coverag...

Continue on
Recent news
ETH +1.65% · · 11h

Ethereum [ETH] can now be used on Amazon

Lightning Network has stepped up its game, now allowing users to transact cryptocurrencies on Amazon. Bitcoin [BTC], Ethereum [ETH], Bitcoin Cash [BCH]...
ETH +1.65% · · 16h

China's mining ban is FUD?

China's mining ban is FUD? China's National Development and Reform Commission (NDRC) is tasked with assessing to recommend, limit, or discontinue industry activities. In the latest assessment…