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1. Symbol is a basic type (also a class) in Ruby. It is a constant and its usage is similar to that of an enumeration type
2. Methods 1 and 2 are equivalent because self refers to this class at this time. Method 1 is generally used because it can avoid the problem of modification when renaming the class, and it can be added to the snippet.
3. attr_accessor生成getter和setter方法。同樣的，attr_reader生成getter，而attr_writerGenerate setter. In Ruby, it is common practice to execute special methods in a class. These methods are generally used to modify (or add) certain features of the class.

1.String is a variable in ruby ??and Symbol is a constant
2. 1 and 2 are the same. @ is a class member. It is very common in Ruby to provide multiple ways of calling a method
3. Equivalent to providing the default getter/setert method

Your question is contextual, I will reply backwards, you may understand it better :)

3. attr_accessor

Execute the code and see the results. Just understand. attr_accessor is a method. After execution, the method will be dynamically added to the class.

This is metaprogramming in ruby. Very awesome said:

module Mod
  attr_accessor(:one, :two)
end
Mod.instance_methods.sort   #=> [:one, :one=, :two, :two=]

1. symbol

In the attr_accessor example just now, symbol (starting with colon) is used.

Why not use strings? Because many methods need to be generated using this method, and a method is a symbol, not a string. In more detail, I learned about the difference between symbol vs. string when I wrote my own Lisp interpreter. Because Ruby supports metaprogramming, it introduces some compiler concepts to enhance the flexibility of the language. This is really awesome.

2. Self is equivalent to calling a method directly, both are calling member methods. What is called with @ is the class method.

That is to say, class methods and instance methods need to be distinguished. class method vs. member method .Many other languages ??also support this difference.

In short, class method can be called without instantiation, while member method must be instantiated before it can be called.

class foo def bar end end
foo.new.bar #調(diào)用實(shí)例方法，必須先new

class foo def self.bar end end 
foo.bar #無需實(shí)例化

ref：http://www.railstips.org/blog/archives/2009/05/11/class-and-instance-methods-in-ruby/

Ruby’s methods are all called through an object, which is called the receiver of the method. The object’s methods are defined in the class to which the object belongs.
How to determine the receiver of a method? The following principles can be followed.
1. When called explicitly, the receiver is obviously the object you gave.
2. Implicitly called methods whose receiver is self.
3.self refers to:
(1) Within a module/class, self refers to the module/class (ruby modules/classes are also objects). Such as
class MyClass
self #Here self is the MyClass object
end
(2) Inside the method, self refers to the receiver of the method. Such as
def method
self #Here self is the receiver used when calling this method
#It is determined when the method is called
end
The ones starting with @ are instance variables, which are two different things from methods.
There is so much knowledge about Ruby that it is difficult to explain clearly in a few words. What is mentioned here is just the tip of the iceberg. Ruby has a very rigorous and complete logic system.

attr_accessor is a statement
Please finish learning the grammar first