From: Brian Adkins <lojicdotcom@...>
Date: 2007-10-26T07:40:13+09:00
Subject: Skip the first invocation e.g. skip_first { foo }

Consider the following code:

first = true
3.times do
  if first
    first = false
  else
    puts 'foo'
  end
  ...
end

I'd like to be able to do the following instead:

3.times do
  skip_first { puts 'foo' }
  ...
end

However, I'm pretty sure that's impossible - especially when you
consider running the above code twice would require state to be
initialized twice, so I expect some initialization outside the loop is
necessary.

So, what's the most elegant way to solve this?

Here are a couple I've come up with minus some implementation details.
They work, but I'm not very pleased with either one. I don't recall
ever needing 'n' to be other than 1, but it feels strange to not
generalize it. I also realize it's more typical to want to execute
code only on the first loop invocation, but I had the opposite need
when this question arose.

# Use an object for state
skip_first = SkipN.new(1)
3.times do
  skip_first.run { puts 'hi' }
  ...
end

# Use a closure for state
skip_first = skipn(1)
3.times do
  skip_first.call lambda { puts 'hi' }
  ...
end

I experimented with using a binding, but I discovered that a new
binding is created each time times invokes the block, so apparently
it's not possible to introduce a variable within the lexical scope of
the block for the duration of the 3.times invocations - or I missed
something.

Brian Adkins