Linking contracts via library contract

Question

The problem involves 3 contracts with an interdependence as follows:
library --> ProductContract --> BillingContract
The contracts are structured as follows: (The DataSet.sol contract below is referenced from a solidity example from: https://github.com/chriseth/solidity-examples/blob/master/iterable_mapping.sol
DataSet.sol:

library DataSet {   
  struct IndexValue { uint keyIndex; uint256 value;}  
  struct KeyFlag { uint key; bool deleted; }  
  struct KeyValue { uint key; uint value; }  

  struct Data {   
      mapping(uint => IndexValue) data;  
      KeyFlag[] keys;  
      //KeyValue[] kvpairs;
      uint size;  
  }  

  function insert(Data storage self, uint key, uint256 value) returns (bool replaced){  
    uint keyIndex = self.data[key].keyIndex;  
    self.data[key].value = value;  
    if (keyIndex > 0)  
      return true;  
    else  
    {  
      keyIndex = self.keys.length++;   
      self.data[key].keyIndex = keyIndex + 1;  
      self.keys[keyIndex].key = key;  
      self.size++;  
      return false;  
    }  
  }  

  function getCurrent(Data storage self) returns(uint index){  
      return self.size - 1;  
  }  

}  

ProductContract.sol:

import "DataSet.sol";  
contract ProductContract {  
    using DataSet for *;  
    DataSet.Data d;  
    mapping (uint => uint) IDToVal;  
    function register (uint p_id, uint val) returns (bool registered) {  
        IDToVal[p_id] = val;  
        registered = true;  
    }  
    function getVal (uint p_id) returns (uint v) {  
         return IDToVal[p_id];  
    }  
}

BillingContract.sol:

import "ProductContract.sol";    
contract BillingContract {  
    ProductContract pc;  
    address PC_Address;  
    function BillingContract (address p) {  
        PC_Address = pc;  
        pc = ProductContract(p);  
    function getVal (uint p_id) returns (uint v) {  
        return pc.getVal(p_id);  
    }  
 }

This results in an error on compiling:

Error: Library "DataSet" declared twice (will create ambiguities during linking).  
    library DataSet {
    ^
Spanning multiple lines.  
The other declaration is here: DataSet.sol:3:1: 
    library DataSet {   
    ^
Spanning multiple lines.
Compiliation failed. See above.  

There is a form of transitive dependence on the above contracts - when I try to use all the contracts in a single '.sol' file, the compilation occurs just fine. Is there a way in which the '.sol' files can be separated and compiled properly? Please advise!

Answer 1

I actually had similar issue in my contract and it was due to the fact that I did not include version pragma in the header :

pragma solidity ^0.4.4;

solved my problem.

hope it helps