Mixing instance_eval and block with arguments

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)
=> #

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?

Kind regards

robert

On Thu, Oct 8, 2009 at 6:04 PM, Robert K.
[email protected] wrote:

s = S.new # or create an instance otherwise

now comes the fun part which does not work

s.instance_eval(1, 2, &init)
=> #

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
=> #
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:[email protected]:43(irb)
irb(main):047:0> s.init(1,2,&init)
=> 11
irb(main):048:0> s
=> #

Don’t know if this is good enough.

Jesus.

On Thu, Oct 8, 2009 at 10:04 AM, Robert K.
[email protected]wrote:

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?

Sounds like you need instance_exec, which is a 1.9 feature but there are
implementations for 1.8:

http://eigenclass.org/hiki.rb?instance_exec

On 10/08/2009 06:52 PM, Jesús Gabriel y Galán wrote:

self.bar = a + 10
context of “self” and pass arguments at the same time. Any ideas how
and extend s with it, or add it to S
=> #

Don’t know if this is good enough.

Thank you! Unfortunately I tried to avoid explicit passing of the
reference.

Kind regards

robert

On 10/08/2009 09:21 PM, Tony A. wrote:

Sounds like you need instance_exec, which is a 1.9 feature but there are
implementations for 1.8:

http://eigenclass.org/hiki.rb?instance_exec

1.9 is OK.

irb(main):001:0> l = lambda {|a| self + a}
=> #<Proc:[email protected](irb):1 (lambda)>
irb(main):002:0> 1.instance_exec(2,&l)
=> 3

Perfect! This is exactly what I need. Thanks a bunch!

This article is so old, I can’t believe I missed this completely.
Amazing: learn something new every day.

Kind regards

robert

This forum is not affiliated to the Ruby language, Ruby on Rails framework, nor any Ruby applications discussed here.

| Privacy Policy | Terms of Service | Remote Ruby Jobs