Weird Ruby Behavior

my_class.rb

class MyClass
  def value
    "VALUE!"
  end
  
  def do_something
    puts value    # Outputs "VALUE!"
    if false
      value = nil    # Should not execute
    end
    puts value    # Outputs nothing
  end
end

MyClass.new.do_something

First call there is no definition of 'value' in the local scope, so it looks up to the instance, and finds the value method.

The interpreter then sees a definition of the 'value = nil' initializing 'value' as a local variable. The last puts outputs the value of 'value'. It's clearer what's happening if you change the 'value = nil' line to 'value = "value"' -- you still get

VALUE!
nil

Local variable assignments in "keyword" blocks always result in that local variable being defined. If you did "for i in []" or "case...when false" it'd work, too. However, "[].each do" would not, nor would any other construct based around an explicit do/end block.

As I understand it, this is sort of an artifact of how local assignments inside "keyword" blocks are made inside the enclosing scope.

Shorter answer: if/case/while/etc. do not create a new scope for local variables, and local variables are defined in these constructs when they are parsed, not when they are executed.