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|
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:
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:
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
Finding Accurate Averages A quick exercise to practice using floats.