1. Variable scope in Ruby
Scope defines where a variable is accessible in the program. Knowing the scope of each variable in the program will be very helpful in avoiding errors and debugging. In Ruby, there are 4 types of scope: local, global, instance and class. Besides Ruby has more Constant variables. In Ruby each variable type has a separate starting character:
| Character starts | Variable scope |
|---|---|
| [az] or _ | Local variable |
| $ | Global variable |
| @ | Instance variable |
| @@ | Class variable |
| [AZ] | Constant |
So you can specify the variable type based only and the first character of the variable. But what about the other way, is to use the defined? method defined?
1 2 3 4 5 | x = "Hello" puts defined? x => local-variable |
2. Local variable
Local variable is a Local variable that begins with the character [az] or _ . The accessibility of the local variable depends on where it is declared. For example, when declaring local variables in a class, mehtod or loop, you will not be able to access local variables outside of that class, method or loop.
1 2 3 4 5 6 7 8 | def helloWorld hello_world = "Hello world!" puts hello_world end helloWorld puts hello_world |
When run will produce results
1 2 3 | Hello world error: undefined local variable or method 'hello_world' for main:object |
2. Global variable
Global variable in Ruby begin with the character $ . Global variables can be accessed from anywhere in the program.
1 2 3 4 5 6 7 | class HelloWorld $hello_world = "Hello world" puts "#{$hello_world} inside class" end puts "#{$hello_world} outside class" |
When run will give results
1 2 3 | Hello world inside class Hello world outside class |
3. Instance variable
Instance variable in Ruby begin with the @ character. It only belongs to an individual object or an object of a class.
1 2 3 4 5 6 7 8 9 10 11 12 13 | class HelloWorld def initialize p @person = p end def speak puts "#{@person} says 'Hello world'" end end hello = HelloWorld.new "Alex" hello.speak |
When run will give results
1 2 | Alex says 'Hello world' |
As the example above we see instance variables only properties for each object and its use scope is entirely in the class.
4. Class variable
Class variable in Ruby begin with the character @@ . Class variable can be accessed in all instances of that class. Another with Global variable operating range is the latest program, Class variable with the scope of activities that are in the class.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 | class HelloWorld @@person = "Alex" def setPerson p @@person = p end def speak puts "#{@@person} says 'Hello world'" end end hello = HelloWorld.new hello.speak hello.setPerson "Micheal" hello.speak |
When run will give results
1 2 3 | Alex says 'Hello world' Micheal says 'Hello world' |
5. Constant
Constant in Ruby begins with a capital letter [AZ] . Constant in Ruby is similar to a variable, but the only thing is that its value is not changed. The Ruby interpreter is not required to fix Constant ‘s value, but if there is a change in Constant ‘s value, the interpreter will notify you of that change.