Ruby Language Variable Scope and Visibility Local Variables
Example
Local variables (unlike the other variable classes) do not have any prefix
local_variable = "local"
p local_variable
# => local
Its scope is dependent on where it has been declared, it can not be used outside the "declaration containers" scope. For example, if a local variable is declared in a method, it can only be used inside that method.
def some_method
method_scope_var = "hi there"
p method_scope_var
end
some_method
# hi there
# => hi there
method_scope_var
# NameError: undefined local variable or method `method_scope_var'
Of course, local variables are not limited to methods, as a rule of thumb you could say that, as soon as you declare a variable inside a do ... end block or wrapped in curly braces {} it will be local and scoped to the block it has been declared in.
2.times do |n|
local_var = n + 1
p local_var
end
# 1
# 2
# => 2
local_var
# NameError: undefined local variable or method `local_var'
However, local variables declared in if or case blocks can be used in the parent-scope:
if true
usable = "yay"
end
p usable
# yay
# => "yay"
While local variables can not be used outside of its block of declaration, it will be passed down to blocks:
my_variable = "foo"
my_variable.split("").each_with_index do |char, i|
puts "The character in string '#{my_variable}' at index #{i} is #{char}"
end
# The character in string 'foo' at index 0 is f
# The character in string 'foo' at index 1 is o
# The character in string 'foo' at index 2 is o
# => ["f", "o", "o"]
But not to method / class / module definitions
my_variable = "foo"
def some_method
puts "you can't use the local variable in here, see? #{my_variable}"
end
some_method
# NameError: undefined local variable or method `my_variable'
The variables used for block arguments are (of course) local to the block, but will overshadow previously defined variables, without overwriting them.
overshadowed = "sunlight"
["darkness"].each do |overshadowed|
p overshadowed
end
# darkness
# => ["darkness"]
p overshadowed
# "sunlight"
# => "sunlight"
