From: Brian Candler <b.candler@...>
Date: 2009-11-17T22:27:13+09:00
Subject: Re: Class inside a Method Body

David A. Black wrote:
> the code is executed as it's encountered, and you get output before
> and after the execution of the method definition. (Of course the
> method body isn't executed until there's an object to which to send
> the "x" method.)

Except: when reading in a source file there is an initial parsing step 
to build the syntax tree, and if that fails then you get a parse error 
and nothing is executed. Mismatched 'end' statements will do that, for 
example.

The difference between parsing and execution is most important when 
considering local variables.

  def x
    puts "In method x"
    99
  end

  def meth1
    x               # << (A)
  end

  def meth2
    x = 123
    x               # << (B)
  end

  def meth3
    if false
      x = 456
    end
    x               # << (C)
  end

  puts "meth1 returns #{meth1.inspect}"
  puts "meth2 returns #{meth2.inspect}"
  puts "meth3 returns #{meth3.inspect}"

The decision as to whether x is a local variable or a method call is 
made statically at *parse* time, before anything is executed. This is 
why at point (C), x is determined to a local variable: there was an 
assignment to x earlier in the method. However at run time that line is 
never actually run so its value is nil.
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