From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2009-10-09T01:52:47+09:00
Subject: Re: Mixing instance_eval and block with arguments

On Thu, Oct 8, 2009 at 6:04 PM, Robert Klemme
<shortcutter@googlemail.com> wrote:
> Hi,
>
> here's what I'd like to do in a silly example:
>
> S = Struct.new :foo, :bar
>
> init = lambda do |a, b|
>  self.foo = b
>  self.bar = a + 10
> end
>
> s = S.new # or create an instance otherwise
>
> # now comes the fun part which does not work
> s.instance_eval(1, 2, &init)
> => #<struct S foo=2, bar=11>
>
> In other words: I like to define a block as an initializer which I can
> store away somewhere and invoke that initializer later on in the
> context of "self" and pass arguments at the same time.  Any ideas how
> I can accomplish this elegantly?

Probably not exactly what you want (can't make self to not be main
inside the lambda), but what about:

irb(main):001:0> S = Struct.new :foo, :bar
=> S
irb(main):003:0> s = S.new
=> #<struct S foo=nil, bar=nil>
irb(main):040:0> def s.init(*args,&blk) #you can put this in a module
and extend s with it, or add it to S
irb(main):041:1> blk[self,*args]
irb(main):042:1> end
irb(main):043:0> init = lambda do |o,a,b|
irb(main):044:1* o.foo = b
irb(main):045:1> o.bar = a + 10
irb(main):046:1> end
=> #<Proc:0xb7d78f18@(irb):43>
irb(main):047:0> s.init(1,2,&init)
=> 11
irb(main):048:0> s
=> #<struct S foo=2, bar=11>

Don't know if this is good enough.

Jesus.