Ruby

Question 1

What is a class?

Answer 1

A blueprint/template for attributes and behaviour of objects

• attributes and instance values
• methods

Question 2

What is an object?

Answer 2

An individual instance of a class

Question 3

What are the three levels of method access control for classes and modules? What do they imply about the method?

Answer 3

Public, Private, Protected

Pu: default, accessible by all instance objects

Pri: can only be called within the scope of an object. E.g. By other methods of the class

No explicit receiver. I.e. Cant be called on object or self

Pro: must be within the scope of an object, can accept an explicit receiver like self, can be called on objects of the same class

NB: explicit receivers

Question 4

What are the three ways to invoke a method in Ruby?

Answer 4

x = Object.new
puts x.some_method

x. send(:some_method)
x. method(:some_method).call

Question 5

Explain this idiom: a ||= b

Answer 5

Conditional assignment

Shorthand for a = a || b

Take notenof boolean case where a = false:

If a = nil or false, it will be assigned b’s value

Question 6

What does self mean?

Answer 6

Gives access to the current object. i.e. The object that is receiving the message

Question 7

What is a block?

Answer 7

A nameless method that can be passed to another method as a parameter

syntax: do…end, {}

Question 8

What is a Proc?

Answer 8

a block of code that can be bound to a set of local variables

Question 9

What is a Lambda?

Answer 9

an anonymous function (of class Proc)

lambda { … }
lambda do … end
-> { … }

argument for higher order functions

Question 10

What is the difference between a proc and a lambda?

Answer 10

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Question 11

What is unit testing? What is a primary technique when doing unit testing?

Answer 11

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Question 12

What is a ruby module?

Answer 12

It is a container for methods and constants

Allows u to mixin and share methods and constants across many classes

“include” is used to mix in a module

Question 13

What is the difference between include, load, require and extend?

Answer 13

Include: methods available to instances (adding instance methods)

Extend: method is available to class itself, not instances of the class

If a module method is prefixed with self it is not accessible by neither a class nor its instances

Question 14

Does ruby support single inheritance or multiple inheritance or both?

Answer 14

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Question 15

What is the difference between:

“and” and “&&”

And

“or” and “||”

Answer 15

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Question 16

What type of variables are there in ruby?

Answer 16

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Question 17

What is the difference between method overloading and method overwriting?

Answer 17

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Question 18

What is a Destructive Method?

Answer 18

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Question 19

What is the difference between a string and a symbol?

Answer 19

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Question 20

What are Enumerator and enumberable?

Answer 20

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Question 21

What is the scope of a local variable?

Answer 21

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Question 22

How does Garbage Collection work in Ruby?

Answer 22

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Question 23

Whats the difference between puts and print?

Answer 23

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Question 24

What are float, dig and max?

Answer 24

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Question 25

What is metaprogramming?

Answer 25

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Question 26

What is the purpose of adding "!" Or "?" At the end of a method name?

Answer 26

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Question 27

What is the difference between a class and a module?

Answer 27

Modules cant be instantiated... more like containers for constants and methods. Can be mixed in to classes Classes can be instantiated. When module is included a proxy superclass is generated to provide access to all methods in module

Question 28

What is meant by "everything is an object" in Ruby?

Answer 28

Ruby doesnt have primitives, and data types are inherited from super classes Methods, operators and blocks are not objects though

Question 29

What are the main aspects of OOP?

Answer 29

Encapsulation Inheritance

Question 30

How does ruby "know" where to get a method that is called on an object?

Answer 30

There is a lookup path that looks up the method in included models and superclasses... ``` [class] [modules] Object Kernel BasicObject ```

Question 31

What does the splat operator * do in method definition and in method calls?

Answer 31

Definition: optional arguments passed as an array E.g def something(x, y, *options) Call: pass an array into method and each element will be passed as if it was passed directly into method

Question 32

What options are available for method arguments?

Answer 32

``` Default values Splat operators for last arg Hash arguments Blocks Keyword arguments Ampersand operator for last arg ```

Question 33

What is the ampersand operator used for in method definition? In method call?

Answer 33

Def: Shows that method expects a block to be passed in A proc will be created and assigned to that parameter Call: a proc object preceded by an ampersand can be passed into a method and the contained block can replace the method using "yield" method