Confusing `method_missing` errors

[coreyward]

Decorum can be hard to develop with because it consumes method_missing errors from further down the call stack. For example, this happens to me a lot:

class House
  include Decorum::Decorations
  # note: no `is_couch?` method
end

class InteriorDecorator < Decorum::Decorator
  def couch
    object.furniture.detect { |f| f.is_couch? }
  end
end

h = House.new
h.decorate(InteriorDecorator)

# Expected:                                     ⇣
h.couch #=> NoMethodError: undefined method `is_couch?` for #<House:0x007fe054553750>

# Actual:
h.couch #=> NoMethodError: undefined method `couch' for #<House:0x007fe054553750>

Dropping a byebug call in couch results in halting execution at the expected point, and causing a method_missing error during the debugging session actually breaks out of it.

Any insight as to how this could be avoided?

Edit: I know, I'm a bad person for using puns in example code and making concepts harder to grok. Sorry.

[erikcameron]

I'm having a hard time reproducing this, though I may not be getting the example. Trying a more basic case:

class Base
  include Decorum::Decorations
end

class Deco < Decorum::Decorator
  def foo
     object.this_method_does_not_exist
  end
end

b = Base.new
b.decorate(Deco)
b.foo  #=> NoMethodError: undefined method `this_method_does_not_exist' for #<Base:0x00000803dab000>
# this is as expected

I thought it might have something to do with it being called on the contents of object.furniture. (Note: It seems like #is_couch? would be defined, or not, in the class(es) of the values contained in object.furniture---probably not instances of House?) I extended the example like this:

class Base
  include Decorum::Decorators
  attr_accessor :furniture
end

class Deco < Decorum::Decorator
  def couch
     object.furniture.detect { |f| f.is_couch? }
  end
end

b = Base.new
b.decorate(Deco)
b.furniture = [1, 2, 3]   # Fixnum definitely doesn't have is_couch?
b.couch   #=> NoMethodError: undefined method `is_couch?' for 1:Fixnum
# again as expected

I'll take a look as soon as I can reliably reproduce it though, you're right, that looks like weird behavior.

[coreyward]

Hmm, I wonder if my issue is related to overlapping method_missing calls. I'm using JsonApiClient and the objects I'm decorating are all instances of a subclass of JsonApiClient::Resource. I'll look more in a bit and try to duplicate in isolation, but if you want to dig further now that's where I'd start.

On Apr 4, 2016, 5:07 PM -0500, Erik Cameronnotifications@github.com, wrote:

I'm having a hard time reproducing this, though I may not be getting the example. Trying a more basic case:

classBaseincludeDecorum::DecorationsendclassDeco<Decorum::Decoratordeffooobject.this_method_does_not_existendendb=Base.newb.decorate(Deco) b.foo#=>NoMethodError: undefined method `this_method_does_not_exist' for #Base:0x00000803dab000# this is as expected

I thought it might have something to do with it being called on the contents ofobject.furniture. (Note: It seems like#is_couch?would be defined, or not, in the class(es) of the values contained inobject.furniture---probably not instances ofHouse?) I extended the example like this:

classBaseincludeDecorum::Decoratorsattr_accessor:furnitureendclassDeco<Decorum::Decoratordefcouchobject.furniture.detect { |f| f.is_couch? }endendb=Base.newb.decorate(Deco) b.furniture=[1,2,3]# Fixnum definitely doesn't have is_couch?b.couch#=>NoMethodError: undefined method `is_couch?' for 1:Fixnum# again as expected

I'll take a look as soon as I can reliably reproduce it though, you're right, that looks like weird behavior.

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