How does CryptoKitties track time?

Question

I'm looking at KittyBreeding.sol and see

 /// @dev Set the cooldownEndTime for the given Kitty, based on its current cooldownIndex.
    ///  Also increments the cooldownIndex (unless it has hit the cap).
    /// @param _kitten A reference to the Kitty in storage which needs its timer started.
    function _triggerCooldown(Kitty storage _kitten) internal {
        // Compute the end of the cooldown time (based on current cooldownIndex)
        _kitten.cooldownEndTime = uint64(now + cooldowns[_kitten.cooldownIndex]);

but I don't see where "now" is defined, except in their kitty-core.test.js

How does this DAPP track time, which lets the website show timers?

https://github.com/axiomzen/cryptokitties-bounty/tree/master/contracts — , Dec 08 '17 at 18:52

score 8 · Accepted Answer · answered Dec 05 '17 at 21:04

8

now is a Solidity special variable, which equates to the current time since the epoch, in seconds.

From the documentation (linked above):

now (uint): current block timestamp (alias for block.timestamp)

answered Dec 05 '17 at 21:04

Richard Horrocks

37,835
13
87
144

score 4 · Answer 2 · answered Dec 05 '17 at 21:23

4

It's worth noting that miners can manipulate now and so it shouldn't be relied upon for anything sensitive such as seeding Psuedo-Random Number Generators.

answered Dec 05 '17 at 21:23

Luke

61
1
1
5

So is tracking delta of block IDs a better way to track units of time? – Dec 06 '17 at 01:35
Agree with Ismael's review but moderators need to be careful about affecting reputation, so even converting this into a comment might be interfering too much. Will leave as is. – eth Dec 06 '17 at 05:01
@quantumpotato It is more secure, as it's harder to game. Btw, here's a real-world scenario where an on-chain Pseudo-Random Number Generator was implemented. It enabled a deterministic trapdoor. – Paul Razvan Berg Jul 29 '18 at 11:23

How does CryptoKitties track time?

2 Answers2