What is a private method in Ruby?
It’s a type of method that you can ONLY call from inside the class where it’s defined.
This allows you to control access to your methods.
A Ruby method can be:
By default ALL your methods are
Anyone can use them!
But you can change this, by making a method
Why is this useful?
Because you can make these methods easier to change.
Imagine you’re writing a code library that is going to be used in a few different projects at work.
When these projects implement your library, they’re going to be calling methods on the classes that you’ve created.
You release a new version…
But you decided to change the name on a
That’s going to produce errors on every project that is using this method!
By having LESS public methods you INCREASE the freedom of change inside your class.
Let’s see a few code examples!
Have you ever seen the “private method called” error message?
self.puts 123 # NoMethodError: private method `puts' called
Then you have tried to use a
private method incorrectly.
You can only use a private method by itself.
It’s the same method, but you have to call it like this.
Private methods are always called within the context of
In other words…
You can only use private methods with:
This means you can’t call private methods from outside the class that defines them.
Because that would require an “explicit receiver”.
You use a method like
send to bypass this rule.
How do you define a
def bacon "private bacon" end private :bacon
private itself is not a keyword, it’s a method defined on the
It’s normal for a class to have more than one private method.
Where do you place these methods?
class Food def public_method end private def bacon end def orange end def coconut end end
Every instance method after
private becomes a private method.
You can use
private_class_method :method_nameif you want to define a class method as private
It’s a common pattern to define all your public methods first, then define your
private methods together at the end of the class.
Public is the default method visibility in Ruby.
Here’s an example:
def orange "Vitamin C" end
If you have an object
food that defines
orange, you can call it like this:
If a method has been made private or protected, you can make it public again.
Protected methods are less common.
They are like
private methods, but you can call them on an object & not just directly.
If you try this example with private you’ll get an error:
class Food def initialize(name) @name = name end def ==(other) name == other.name end protected attr_reader :name end food = Food.new("chocolate") puts food == food
You get the error because
name would be private so you can’t do
protected this code works!
That’s the difference, the fact that
protected keeps the method
private, but it also allows you to call that method on an object.
With private you can only do
name, with protected you can do
When should you use protected?
Only if you have a very specific case, like the equals (
The Ruby documentation recommends using
private instead of
protected whenever possible.
And there’s this note:
“A protected method is slow because it can’t use inline cache.”
I was curious about this so I ran some benchmarks:
public: 2813891.9 i/s private: 2699273.8 i/s protected: 2572122.0 i/s
That’s a difference of 8.5% in performance.
You’ve learned about Ruby method visibility, public, private & protected methods. These aren’t Ruby keywords, they are methods themselves defined on the
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Thanks for reading 🙂