Timezones and Offsets

So far, we've seen examples of how to use dates and times in Ruby. 0:00 However, there's a lot more that we haven't taken into account, 0:05 things like time zones, offsets, daylight savings, and more. 0:09 Let's go into a bit more depth with dates and times now using Workspaces. 0:14 When we've been working with dates and times so 0:20 far, we haven't been worrying too much about time zones. 0:22 Different parts of the world use something called an offset 0:26 when taking time into account. 0:29 You probably have friends or relatives in a different time zone and may need to 0:30 mentally subtract or add hours so that you can call them at a reasonable time of day. 0:34 Now, the same thing happens in Ruby and 0:39 all programming languages when you're working with time zones. 0:41 Now, luckily there are only a few different time zones that we 0:44 have to deal with. 0:47 No, I'm just kidding. 0:49 There are a lot of different time zones in the world. 0:50 Each different one on this map is denoted by a vertical bar. 0:53 Now, we have just a ton of different time zones, and 0:59 you'll notice that they're represented using UTC and an offset, 1:01 and the offset is different depending on where exactly you are in the world. 1:08 So here's a list of time zones, but let's go ahead and 1:14 see how that works using Ruby. 1:17 Now, when we instantiate a new time object, 1:20 if we're not using time.now or time.new, we can specify it as the last argument. 1:24 So by default, let me go ahead and launch IRB here. 1:30 So by default, if we did a time.new, 1:37 it's going to use the time zone wherever the computer is. 1:40 Now, since we're using Workspaces, these servers default to UTC time, 1:45 which means if we want to create a time in a different time zone, 1:49 we need to explicitly tell Ruby that. 1:53 So I'm going to create this variable called time1. 1:56 And we'll say that's equal to the new time. 1:59 It's the year 2014. 2:04 It's July 1st at 12 o'clock. 2:06 And I'm going to use the offset four hours from UTC time. 2:09 So now we have that. 2:16 We have that into account, and we can see this time is different. 2:19 It says minus 0400. 2:22 Well, let's go ahead and see how that compares to another time. 2:24 And let's put that time, same day, 2:30 but with a five-hour offset. 2:38 Now, if we look at these two times, we can see time1 is not equal to time2. 2:43 But let's change time2. 2:49 Now, we're going to change this to be 11 o'clock. 2:54 With that same offset. 2:59 Now when we do that. 3:03 It's the same time as the other object, just in a different time zone. 3:08 Now, to make matters worse when dealing with times and time zones, 3:15 as if this wasn't confusing enough, some parts of the world add or 3:19 subtract an hour if a certain time takes place in daylight savings time. 3:22 Now, Ruby luckily allows us to answer this question if we're talking to a time object 3:27 to see if it took place during daylight savings. 3:32 We can do that by saying daylight savings time, with a question mark. 3:35 And if we look in the documentation, we can see this returns true if 3:42 the time occurs during daylight savings time in its time zone. 3:47 Now, when we're working with times, we can convert any time to UTC. 3:53 And we do that by using the UTC method. 3:58 Now, this will modify the time instance, so 4:03 if we want to have an unmodified time instance, we'll convert that. 4:06 So we'll say time1, and the dup method duplicates an object. 4:10 So if we did time1 and UTC, 4:17 we can see that this changes from 12 to 16 and 4:20 UTC, rather than having an offset of some sort. 4:25 Now, if we're looking at this UTC time1 object. 4:37 We can call this UTC offset method to see how far it 4:44 is from the Universal Time Zone. 4:47 And if we took a look at time1 and called the same method, 4:50 we can see it return this 14,400 number. 4:55 And that's the number of seconds. 4:59 We could convert that to hours, 5:03 which we would be more familiar with by dividing by 60, twice. 5:04 It's important to keep time zones and 5:09 offsets in mind when working with dates and times. 5:11 There are some gems that make this a little bit easier, but for right now, 5:15 just try manipulating and changing times on your own, using a Workspace. 5:18