Calling Methods on an Object

[MUSIC] 0:00 [SOUND] In this stage, we're going to learn how to call methods on an object. 0:02 To be clear, we're not talking about passing an argument to a method. 0:08 We mean taking a piece of data and 0:12 calling a method that is only available on that piece of data. 0:14 For example, strings have one set of methods available on them, and 0:18 numbers have a different set of methods. 0:22 Almost every type of data available in Ruby has a large set of methods you 0:25 can call on it. 0:29 How large? 0:30 Any given string is going to have over 170 different methods. 0:32 A number is going to have over 130. 0:36 Don't worry, we're not going to try and teach you all of those methods right now. 0:39 You'll only use a small portion of them on a regular basis. 0:43 But it is important to understand how to call methods on an object, and 0:47 that's just what this stage will show you. 0:51 When you call a method, it's important for Ruby to know which object you're calling 0:54 it on, because the behavior of the method will vary based on the object. 0:58 We type the dot operator following an object to indicate that we're calling 1:02 a method on it. 1:06 So here you see a dot operator 1:07 that indicates that we're calling the length method on this string, "AA". 1:10 Here's another dot operator that indicates we're calling the length method on this 1:15 string instead. 1:19 And the result of the length method varies for these two different strings, 1:20 because obviously they have different lengths. 1:24 The first output's a length of 2, the second one output's a length of 9. 1:26 And here you see the data operator being used with several numbers. 1:30 So we call the odd method on the number 3, and 1:34 since 3 is odd and not even, that returns true down here. 1:38 By the way, question mark is a valid character at the end of a method name, 1:43 and so is exclamation point. 1:48 These two symbols are valid only at the very end of a method name. 1:49 This feature is unique to Ruby. 1:53 It's a little unusual for programming languages. 1:54 The question mark doesn't have any special meaning to the Ruby language itself but 1:57 by convention, a question mark usually means that a method is going to return 2:02 either true or false. 2:05 The same is true for this even method down here. 2:06 Here, we call the even method on the number 3. 2:09 And since 3 is odd and not even, 2:12 obviously that's going to return false down here at the output. 2:13 Likewise, if we do call dot even on the number 4, well, 2:18 4 is even so that is going to return true. 2:22 In place of the object itself, we can use a variable that refers to the object. 2:26 So if we wanted, instead of saying "AA".length, 2:30 we could sign the string "AA" to a variable named string, 2:35 and then we can print the length of the value that stored in the string variable. 2:40 So let's do that in place of put this "AA".length here, and 2:47 get rid of all this, and we can also do the same with a number. 2:51 Let's create a variable named, number. 2:56 We'll assign it number 4, and we'll call the even method 2:58 on the value that's stored in the number variable. 3:03 Save that, try running it. 3:09 Oops, I made a typo, one second. 3:13 You'll notice that it gave me an error down here. 3:17 Reporting an undefined method while obviously there's no method name to pute. 3:20 So we're gonna change that to puts, try rerunning it again. 3:25 There we go. 3:30 And now, we get length of 2 for the value stored in the string variable. 3:31 And we get a value of true for 3:36 calling the even method on the value stored in the number variable. 3:38 You can also chain method calls together. 3:43 Let's suppose we wanna know whether a string contains an even number of 3:45 characters. 3:48 Well, we can call length on the string, and 3:49 then call even on the number return from length. 3:52 Let's try that. 3:54 For our first attempt here, we're going to store everything in variables. 3:55 So we'll say string = "AA", and then we'll create a variable named length, 3:59 And store the value returned from calling a string.length in that. 4:07 And then we can print the result of calling, 4:13 The even method on the value that's stored in length. 4:20 This is one way we can do it. 4:24 Let's try running this, and we get tricked because there are two 4:25 characters in the string "AA", and that is of course an even number. 4:30 But there's a shorter way to do this, we can simply print out the result of 4:35 calling, string.length, which will return a number. 4:39 And then calling.even on that return value. 4:44 And then we can get rid of all this other code. 4:49 And if we try rerunning this, we'll get the exact same result, it's true. 4:51 string.length returns the value 2, and 2 is an even number. 4:55 You should only chain methods in situations where you're sure the first 5:01 method call won't fail, otherwise, subsequent methods will return an error. 5:04 But you'll often see this done in Ruby code, so 5:08 it's good to be aware of the technique. 5:11