Forum: Ruby instance_eva()l-ing a proc with parameters

Dear friends,

I need to evaluate a proc within an instance context and would like to
pass it a parameter. The only straight forward way I found is to use
instance_eval(), however it does not allow to pass parameters to a proc,
only the instance itself is passed as a single parameter:

[rh-30-x86.irvspxl08:1004]gbystrit> irb
irb(main):001:0> [ VERSION, PLATFORM ]
=> ["1.8.4", "i686-linux"]
irb(main):002:0> block = proc { |*_args| puts _args.inspect }
=> #<Proc:0xb75b21fc@(irb):2>
irb(main):003:0> class A; end
=> nil
irb(main):004:0> a = A.new
=> #<A:0xb75a9674>
irb(main):005:0> a.instance_eval &block
[#<A:0xb75a9674>]
=> nil
irb(main):006:0> a.instance_eval 1, 2, &block # Hypothetical
ArgumentError: wrong number of arguments (2 for 0)
        from (irb):6:in `instance_eval'
        from (irb):6
        from :0

Is there any easy way to do what I want? I also found that I can use
define_method() to turn a proc into an instance method and then call it
with parameters, however it involves a lot of hassle (for one,
define_method() is private).

Any thoughts?

Thank you,
Gennady Bystritsky.

On Tue, Oct 03, 2006 at 01:35:48AM +0900, Gennady Bystritsky wrote:
> Dear friends,
> 
> I need to evaluate a proc within an instance context and would like to
> pass it a parameter. The only straight forward way I found is to use
> instance_eval(), however it does not allow to pass parameters to a proc,
> only the instance itself is passed as a single parameter:
Google for instance_exec, there are various and sundry implementations,
including one built into rails.

http://eigenclass.org/hiki.rb?instance_exec has various implementations
and their respective strengths and weaknesses. Or you can just use ruby
1.9 where it's part of the core.