Kernel.xxx interferes with method_missing

ruby-talk
1

Hello!

I'm using method_missing to create DSL, the problem is that Kernel.xxx
methods are interferes with it.
How this issue can be solved?

It seems that one solution is to explicitly define all global methods
(p, select, ...) on the target class for method_missing.

But i hope there is more elegant solution :). Maybe some trick with
sandboxes?

CODE:
  class Parameters # < BlankSlate
    attr_reader :result

    def initialize &block
      @result = {}
      instance_eval &block
    end

    def method_missing m, *p
      @result[m] = *p
    end
  end

  describe do
    it do
      hash = Parameters.new do
        one 1
        select1 'Select' # <= Problem here, it calls Kernel.select
      end.result

      hash.should == {:one => 1, :select1 => 'Select'}
    end
  end

···

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2

Small error in code, 'select' not 'select1' :).

···

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3

On Ruby 1.9, use BasicObject. On Ruby 1.8, use Jim Weirich's
BlankSlate object. I recently ran into an issue with blankslate
though where it was incorrectly revealing methods, so you might want
to use my patched version:

http://pastie.org/377487.txt

Take this with a shaker of salt though, I mainly modified the example
to show off certain dynamic programming techniques in my book[0], and
not necessarily to make it robust. I have emailed Jim about these
changes, but he hasn't gotten back to me yet.

-greg

···

On Mon, Feb 2, 2009 at 12:11 PM, Alexey Petrushin <axyd80@gmail.com> wrote:

Hello!

I'm using method_missing to create DSL, the problem is that Kernel.xxx
methods are interferes with it.
How this issue can be solved?

It seems that one solution is to explicitly define all global methods
(p, select, ...) on the target class for method_missing.

But i hope there is more elegant solution :). Maybe some trick with
sandboxes?

4

Whoops...

On Mon, Feb 2, 2009 at 12:56 PM, Gregory Brown

Take this with a shaker of salt though, I mainly modified the example
to show off certain dynamic programming techniques in my book[0], and
not necessarily to make it robust. I have emailed Jim about these
changes, but he hasn't gotten back to me yet.

[0] http://rubybestpractices.com

Sorry for the shameless plug, but it's directly relevant to the OP's
questions since I cover these topics in the book, and it will be under
a creative commons license 9 months after it hits the shelves.

-greg

5

Possible solution, a hack with redefining all global methods.

  class ExtraBlankSlate < BlankSlate
    CUSTOM_UNDEFINE = [:p, :select, :puts]

    undefine = Kernel.instance_methods + Object.instance_methods +
CUSTOM_UNDEFINE
    BlankSlate.instance_methods.each{|m| undefine.delete m}

    undefine.each do |m|
      script = %{\
  def #{m} *p, &b
    method_missing :#{m}, *p, &b
  end}
      class_eval script, __FILE__, __LINE__
    end
  end

···

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