From: Eric Mahurin <eric_mahurin@...>
Date: 2005-09-28T22:33:43+09:00
Subject: Re: creating independent lambdas in loops

--- ts <decoux@moulon.inra.fr> wrote:

> >>>>> "M" == Michael Roth <mroth@nessie.de> writes:
> 
> M>     a = []
> 
> M>     for multi in [2, 3, 4, 5]
> M>       a << lambda do |n|
> M>         n * multi
> M>       end
> M>     end
> 
>        [2, 3, 4, 5].each do |multi|
>           a << lambda do |n|
>              n * multi
>           end
>        end

The each loop works because the variable multi is local to the
each block.  Each iteration through that block will use a
different variable multi.

To me, it seems like a bug that the for loop isn't equivalent
to the each loop.  I think it is putting multi in the
surrounding scope because of the syntactic order - multi comes
before the Enumerable.

You'll see the same problem if you assign multi before the each
loop.  If you wanted to continue using the for loop (or multi
was already used), you could make a localized version of it
like this:

a = []
for multi in [2, 3, 4, 5]
  lambda do |multi_local|
    a << lambda do |n|
      n * multi_local
    end
  end.call(multi)
end
for mul in a
  puts mul.call(17)
end

I didn't realize that within a block, the only variables truly
local are the argument variables.  I think I've read somewhere
that in the future ruby will put better facilities in for
controlling variable scope locality.

> M>     for mul in a
> M>       puts mul.call(17)
> M>     end



		
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