Can I retrieve the timestamp the contract was mined on, inside of the contract?

Question

I'm aware of the now keyword that aliases block.timestamp (uint): current block timestamp and the time units

But I fail on finding a way to get the block timestamp of when the contract was mined. Should I use an event and "log" the now keyword into a start variable ?

Answer 1

You have to code it into your contract either by saving the block.timestamp in the constructor:

contract A {
  uint public createdTimestamp;
  function A() {
    createdTimestamp = block.timestamp;
  }
}

which you can access like this:

contract B is Test {
  function testTimestamp () {
    A a = new A();
    uint timestamp = a.createdTimestamp();
    //@log timestamp `uint timestamp`
  }
}

or log an event, if you don't need to access this information from within the chain:

contract A {
  event created(uint timestamp);
  function A() {
    created(block.timestamp);
  }
}

But a query for arbitrary contracts is not possible, however this can be achieved in O(log_2 n) with a binary search for contract code.