Modifiers

simpleModifierExample.sol

pragma solidity ^0.4.15;

contract Example {

  address public owner;

  function Example () {
    owner = msg.sender;
  }

  modifier throwForInvalidAddress (address target) {
    if (target == 0x0) revert();
    _;
  }

  modifier isAllowed () {
    assert(msg.sender == owner); // contract state
    _;
  }

  modifier isValueBiggerThanZero(uint value) {
    require(value > 0);
    _;
  }
  
  function isOwner(address target) constant returns (bool) {
    return target == owner;
  }

  function simpleFunction(address target) 
    throwForInvalidAddress(target)
    isValueBiggerThanZero(msg.value)
    isAllowed // omitted parenthesis for parameterless modifiers
    payable
  {
    // do something
  }
}