From: Morton Goldberg <m_goldberg@...>
Date: 2007-10-26T08:18:28+09:00
Subject: Re: Skip the first invocation e.g. skip_first { foo }

On Oct 25, 2007, at 6:40 PM, Brian Adkins wrote:

> 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.

It's not entirely clear to me what you are trying to accomplish, so  
this may way off base.

For some reason you are ignoring that Integer#times passes an index  
into its block, but if are willing to make use of this index, what  
you propose can be written as

3.times { |i| puts "hi" if i > 0 }

Regards, Morton