61 lines
2.0 KiB
Markdown
61 lines
2.0 KiB
Markdown
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---
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title: True, False, and Nil
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---
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<h1>True, False, and Nil</h1>
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`true`, `false`, and `nil` are special built-in data types in Ruby. Each of these keywords evaluates to an object that is the sole instance of its respective class.
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```ruby
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true.class
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=> TrueClass
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false.class
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=> FalseClass
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nil.class
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=> NilClass
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```
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`true` and `false` are Ruby's native boolean values. A boolean value is a value that can only be one of two possible values: true or not true. The object `true` represents truth, while `false` represents the opposite. You can assign variables to `true` / `false`, pass them to methods, and generally use them as you would other objects (such as numbers, Strings, Arrays, Hashes).
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`nil` is a special value that indicates the absence of a value: it is Ruby's way of referring to "nothing". An example of when you will encounter the `nil` object is when you ask for something that doesn't exist or cannot be found:
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```ruby
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hats = ["beret", "sombrero", "beanie", "fez", "flatcap"]
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hats[0]
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=> "beret" # the hat at index 0
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hats[2]
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=> "beanie" # the hat at index 2
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hats[4]
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=> "flatcap" # the hat at index 4
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hats[5]
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=> nil # there is no hat at index 5, index 5 holds nothing (nil)
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```
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Zero is not nothing (it's a number, which is something). Likewise, empty strings, arrays, and hashes are not nothing (they are objects, which happen to be empty). You can call the method `nil?` to check whether an object is nil.
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```ruby
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0.nil?
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=> false
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"".nil?
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=> false
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[].nil?
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=> false
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{}.nil?
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=> false
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nil.nil?
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=> true
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# from the example above
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hats[5].nil?
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=> true
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```
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Every object in Ruby has a boolean value, meaning it is considered either true or false in a boolean context. Those considered true in this context are "truthy" and those considered false are "falsey." In Ruby, <em>only</em> `false` and `nil` are "falsey," everything else is "truthy."
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<h3>Other Resources</h3>
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* https://ruby-doc.org/core-2.3.0/TrueClass.html
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* https://ruby-doc.org/core-2.3.0/FalseClass.html
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* https://ruby-doc.org/core-2.3.0/NilClass.html
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* https://en.wikipedia.org/wiki/Boolean
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