From: Rolf Timmermans <molfie@...>
Date: 2011-01-17T19:25:40+09:00
Subject: Obscure syntax error

Hi all,

Today I came across a very strange scenario that raises a syntax error in pretty much all Ruby implementations. I have absolutely no explanation for the following behaviour:

x :y
#=> bar.rb:1:in `<main>': undefined method `x' for main:Object (NoMethodError)

x = nil
x "y"
#=> bar.rb:2:in `<main>': undefined method `x' for main:Object (NoMethodError)

x = nil
x :y
#=> bar.rb:2: syntax error, unexpected ':', expecting $end

Why does that latter case raise a syntax error during parsing? Why would this be invalid Ruby? Why is it only invalid when supplying a symbol argument, and why only when the local variable with the same name is already defined? I would expect all three examples above to be run and abort with a NoMethodError.

The behaviour is consistent in Rubinius, JRuby, Ruby 1.9 and Ruby 1.8. What's going on, does anyone know?


Kind regareds,

Rolf Timmermans