method_missing Within instance_eval

Question

Full code: http://friendpaste.com/5TdtGPZaEK0DbDBa2DCUyB

class Options
    def method_missing(method, *args, &block)
        p method
    end
end

options = Options.new

options.instance_eval do
    foo
    foo = "It aint easy being cheesy!"
end

puts "#===---"
options.foo
options.foo = "It still aint easy being cheesy!"

This returns:

:foo
#===---
:foo
:foo=

Because it is treating foo = "" as a local variable within instance_eval, it's not recognize it as a method.

How would I make instance_eval treat it as a method?

To be captured within method_missing for me to manipulate it, specifically to set a key/value in a hash. It'll kinda work like a Struct. — RyanScottLewis
– RyanScottLewis, Commented Dec 16, 2009 at 22:00

Chuck · Accepted Answer · 2009-12-16 22:03:51Z

5

The expression foo = "" will never be a method call. It is a local variable assignment. This is a fact of Ruby's syntax. In order to call a setter, you have to specify a receiver explicitly. This is why most Ruby pseudo-DSLs use the Dwemthy-style:

class Dragon < Creature
  life 1340     # tough scales
  strength 451  # bristling veins
  charisma 1020 # toothy smile
  weapon 939    # fire breath
end

That avoids the equals sign problem.

answered Dec 16, 2009 at 22:03

Chuck

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1 Comment

RyanScottLewis Over a year ago

Oh geez, why didn't I think of this? Thats perfect =D

mckeed · Accepted Answer · 2009-12-16 21:12:37Z

2

Do self.foo = "" to make it treat it as a method.

answered Dec 16, 2009 at 21:12

mckeed

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4 Comments

RyanScottLewis Over a year ago

Yeah, that would work I suppose. But the reason I'm trying to figure this out is so I don't have to use self.foo or options.tap { |o| o.foo } to run methods =/

RyanScottLewis Over a year ago

Here is my full code, if you are intersted: friendpaste.com/5TdtGPZaEK0DbDBa2DCUyB

mckeed Over a year ago

Sadly, I don't think it is possible. foo = will always be interpreted as a local variable assignment and there is no way of getting to local variables defined inside a block.

RyanScottLewis Over a year ago

It seems even foo=() will not work. Oh well, I guess I will have to do it your way. Thanks

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