Local Variable Scope

The scope of a variable indicates where in a program a particular variable is available for use.

A variable’s scope is defined by where the variable is initialized (or created).

In Ruby, the scope of a variable is determined by a block, or a piece of code after a method invocation, usually delimited by curly braces {} or do/end ¹ .

Inner Scope and Outer Scope

The concept of inner scope and outer scope is dependant of the context in which they are referenced. Like the name suggest, the inner scope is inner relative to the outer scope.

For example, let’s say we have a program in a text file. The program inside has a block. Relative to the program (outer scope), inside the block is the inner scope.

Now, if in this block we have yet another block, this second block will be the inner scope, relative to the first block which becomes itself a outer scope.

That being said, the important point is:

Inner scope CAN access variables initialized in an outer scope but a outer scope CAN’T access variables initialized in an inner scope.

Example

a = 9    # Integer 9 assigned to variable a in the outer scope

loop do  # Method invocation with a block
  a = 5  # Integer 5 assigned to variable a in the inner scope
  b = 3  # Integer 3 assigned to variable b in the inner scope
  break
end

puts a  # => 5
puts b  # => undefined local variable or method `b'

Source: Variable Scope, Introduction to Programming with Ruby

Footnotes

Not all do/end pairs imply a block: Deciding Whether Part of a Code is a Block or Not

Links to this page

What is self in Ruby

We know we need setter methods (provided by attr_accessor) to modify the @name and @age instance variables. However, in the change_info method we are not calling those two setter methods. Instead, we are initializing new local variable name and age. As thoses are scoped to the method scope (see also Local Variable Scope), they cease to exist when the method returns.
Variable Shadowing

The variable in the inner scope shadows the variable with the same name in the outer scope, making the latter inaccessible in the inner scope, although it should be (see Local Variable Scope).
Variable Scope in Object Oriented Programming

The rule of variable scope if different than that of Local Variable Scope although it shares some similarity. First we need to distinguish scope of instance and class (and constants).
Type of Variables

See Variables as Pointers and Local Variable Scope.
Study Guide for Test

Local Variable Scope
Software

Local Variable Scope
Ruby’s Proc and its Scope

We know from Local Variable Scope that variable initialized outside a method definition aren’t accessible inside the method. But the code above clearly knows about the animal local variable.
Methods in Java

Variables in Java are scoped to the method they where declared. See also Local Variable Scope.
Method Definition and Method Invocation

The rules of Local Variable Scope for block inside a method definition do translate.
Deciding Whether Part of a Code is a Block or Not

In Ruby, variable scope is defined by a block (see Local Variable Scope). A block is usually delimited by curly brace {} or do/end pair.

2020-09-15T23:22