From: Mike Austin <mike_ekim@...>
Date: 2010-05-05T15:35:07+09:00
Subject: for-in vs. map closures

I was experimenting with closures and JavaScript's and Ruby's
behavior.  Ruby seems to close over its arguments automatically if
using map:

[1, 2, 3].map { |n| lambda { n * n } }.map { |b| b.call() }  # [1, 4,
9]

But using "for" iteration, returns a different result:

a = []
for n in [1, 2, 3] do a << lambda { n * n } end
a.map { |b| b.call() }  # [9, 9, 9]

This is also the behavior in JavaScript, which frequently catches
developers off guard when attaching event handlers to elements.

Can anyone explain the difference?  Is map creating a new anonymous
function every iteration?

Mike