From: Josh Cheek <josh.cheek@...>
Date: 2011-11-14T12:16:37+09:00
Subject: Re: Binding#with

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On Sun, Nov 13, 2011 at 8:30 PM, Intransition <transfire@gmail.com> wrote:

> Binding#with
>
>     def with(_local_variables)
>       eval("Proc.new{ |#{_local_variables.keys.join(',')}| binding
> }").call(*_local_variables.values)
>     end
>
> Try it:
>
>     b = binding.with(:a=>1)
>     b.eval('a')  #=> 1
>
>
Note I had to explicitly define this in Binding to avoid the private method
invocation.


> Now, it there a way to add a "yield" to the binding? I tried:
>
>   def with(_local_variables, &_yields)
>     eval("lambda{ |#{_local_variables.keys.join(',')},&yields| binding
> }").call(*_local_variables.values, &_yields)
>   end
>
>     b = binding.with{ |x| x+x}
>     b.eval('yields[1]')  #=> 2
>
>
Note that this didn't work for me unless I passed a hash to Binding#with,
because otherwise the syntax it generates looks like `lambda{ |,&yields|
binding }` which is a syntax error


> but
>
>     b.eval('yield(1)')  #=> Error
>
>
Seems doubtful, b/c I think `yield` only exists in methods, not in procs
(this is just based on behaviour I've experienced, not on an implementation
level knowledge)

def l() yield 1 end
method(:l).call { |x| x + x } # => 2

vs

lambda { yield 1 }.call { |x| x + x }
# ~> -:1:in `block in <main>': no block given (yield) (LocalJumpError)

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