Solidity Libraries Example 1

pragma solidity ^0.4.11;

library SetLib {
  // This will define a whole new struct data type which is going
  // to be used for holding its data inside the calling contract.
  struct LibData { mapping(uint => bool) flagsMapping; }

  // Notice how the first parameter's type is "storage
  // reference" therefore it is only its storage address instead of
  // its contents being passed along with the call. That is the
  // Library functions' special feature. Calling the first
  // parameter "selfStore" is idiomatic, if it happens so that the 
  // function can be seen as that object's.
  function insertData(LibData storage selfStore, uint value)
      returns (bool)
  {
      if (selfStore.flagsMapping[value])
          return false; // is already there
      selfStore.flagsMapping[value] = true;
      return true;
  }

  function removeData(LibData storage selfStore, uint value)
      returns (bool)
        {
      if (!selfStore.flagsMapping[value])
          return false; // is not there
      selfStore.flagsMapping[value] = false;
      return true;
  }

  function contains(LibData storage selfStore, uint value)
      returns (bool)
  {
      return selfStore.flagsMapping[value];
  }
}

contract Cont {
    SetLib.LibData valuesKnown;

    function registerData(uint value) {
        // The functions of the library may be called without a
        // certain instance of the library, because the
        // "instance" is going to be the current contract.
        require(SetLib.insertData(valuesKnown, value));
    }
    // Inside this contract, it's possible to directly access valuesKnown.flagsMapping too, in case we want.
}