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Alex Kuhl
Alex Kuhl

Reputation: 1824

Calling .methods on class vs instance in Ruby

Hoping to poll the collective consciousness here since I can't structure this in a way to find an answer via search. In Ruby 1.9+, calling .methods on an instance will yield different results than on the class of that instance. For example, "foo".methods will include 'length' and 'size' whereas String.methods will not. What is the reason for this? I am a veteran programmer but new to Ruby. From my understanding, methods is supposed to include all ancestor methods, so is it through a mixin or some other pattern that length and size are added into the instance's list but not the class's?

Upvotes: 1

Views: 240

Answers (2)

Dave Newton
Dave Newton

Reputation: 160181

Length and size are String instance methods, why would they be included in a list of String's (a class) methods? Classes are objects and have their own methods.

In other words, you get the list of methods supported by the object you're calling it on. String is a class, so you get its specific class methods, plus class methods it inherits.

A string instance is an instance, so you get string's instance methods, and instance methods it inherits.

Upvotes: 2

Richard JP Le Guen
Richard JP Le Guen

Reputation: 28753

You're confusing .methods() with .instance_methods().

The first will give you the methods which can be invoked on the String object - that is the String class as an object itself. The second will give you the methods of objects created using the String class, or instances of String.

Upvotes: 2

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