Ruby uses special names for things that we already know. For instance, it uses the word Float to mean “decimals”. Here are more definitions:
- Object: That’s just any piece of data. Like the number 3 or the string ‘hello’.
- Class: Ruby separates everything into classes (or categories), such as integers, floats and strings.
- Method: These are the things that you can do with an object. Think of it as the object’s “behaviour”. For example, you can add integers together, so + is an integer method. You can capitalize strings, so upcase is a string method.
You’ve already seen three classes for things that you already know (note that Ruby class names are capitalized):
| Old name | Ruby class |
|---|---|
| integer | Integer |
| decimals | Float |
| text | String |
You have also seen several methods:
| Ruby class | Some methods |
|---|---|
| Integer | + – / * % ** |
| Float | + – / * % ** |
| String | capitalize, reverse, length, upcase |
Classes vs. objects¶
Make sure you understand the difference between classes and objects. An object is a unit of data. A class is what kind of data it is.
For example, 3 and 5 are different numbers. They are not the same object. But they are both integers, so they belong to the same class. Here are more examples:
| Object | Class |
|---|---|
| 2 | Integer |
| -5 | Integer |
| 7.2 | Float |
| 3.14 | Float |
| ‘hello’ | String |
| ‘world’ | String |
Class#method notation
Remember, different classes have different methods. Here are some differences that you have already seen.
- Division (/) doesn’t work the same with integers and floats.
- Addition (+) doesn’t work the same with strings as it does with integers.
- Strings have several methods that integers and floats don’t have (e.g., capitalize, length, and upcase).
For this reason, we will use the notation Class#method to state exactly which method we mean. For instance, I will say Integer#+ to differentiate it from Float#+ and String#+. I can also say that String#upcase exists, but Integer#upcase does not exist.
Converting between classes¶
Ruby has some methods for converting between classes:
| Method | Converts | |
| From | To | |
| String#to_i | String | Integer |
| String#to_f | String | Float |
| Float#to_i | Float | Integer |
| Float#to_s | Float | String |
| Integer#to_f | Integer | Float |
| Integer#to_s | Integer | String |
Examples:
shell> irb --simple-prompt
>> 34.to_s
=> "34"
>> "12".to_i
=> 12
>> "hello".to_i
=> 0
>> 27.2.to_i
=> 27
>> 3.to_f
=> 3.0
Exercises¶
Finding Accurate Averages A quick exercise to practice using floats.
