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comp.lang.ruby

Kernel.xxx interferes with method_missing

Alexey Petrushin

2/2/2009 5:12:00 PM

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
--
Posted via http://www.ruby-....
4 Answers

Alexey Petrushin

2/2/2009 5:14:00 PM

0

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

2/2/2009 5:56:00 PM

0

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?

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/...

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

Gregory Brown

2/2/2009 5:58:00 PM

0

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://rubybestpra...

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

Alexey Petrushin

2/3/2009 6:32:00 AM

0

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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