To build a wiki-like engine (or DSL) with dynamically generated
methods, I do the following :
class Base
def self.match(name, regexp, &block)
define_method(name) do |text|
text.gsub!(regexp) do
puts "$1 in match method : #{$1}"
#block.call
instance_eval(&block)
end
end
end
end
class Foo < Base
match :g, /(.)g$/i do
puts "$1 in passed block : #{$1}" #Unfortunately $1 is lost !
'ggg' #so only hardcoded values 
end
end
f = Foo.new
f.g('bla') #bla
f.g('doing') #doiggg ; problem is I cannot use $1 in block
After some research I found these 2 links
http://eigenclass.org/hiki/binding.of_caller+substitute
http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/202600
(BTW I am trying to avoid any third-party libraries)
But I don't manage to get these to work...
I need to get $1, $2, etc. special values
in the block I pass in Base subclasses.
How can I do that ?
Thanks,
Vincent
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f.g('doing') #doiggg ; problem is I cannot use $1 in block
# maybe pass it as a parameter or save it away to some global variable
or 'per thread' variable.
-R
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I finally managed to get it to work :
class Base
def self.match(name, regexp, &block)
define_method(name) do |text|
puts "#{text}"
text.gsub!(regexp) do
#hack to restore magical $~ (and so $1, $2, etc.) in block
eval('lambda{|x| $~ = x}', block).call($~)
block.call #or instance_eval(&block)
end
puts "=> #{text}"
end
end
end
class Foo < Base
match :g, /(.)g$/i do
$1.upcase + '_ggg'
end
end
f = Foo.new
f.g('bla')
f.g('doing')
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Vincent L. wrote:
class Foo < Base
match :g, /(.)g$/i do
puts "$1 in passed block : #{$1}" #Unfortunately $1 is lost !
'ggg' #so only hardcoded values 
end
end
...
But I don't manage to get these to work...
I need to get $1, $2, etc. special values
in the block I pass in Base subclasses.
How can I do that ?
The backref and numbered group globals are tied to the containing method/class body. So here, where you have a match call with a block inside a class body, the capture would be the one that lives in that body. That's part of the problem with relying on these special variables and the side effect of e.g. gsub: you can't implement the same behavior in Ruby because certain core methods like gsub have "special" side effects impossible to emulate.
- Charlie
Vincent L. wrote:
I finally managed to get it to work :
class Base
def self.match(name, regexp, &block)
define_method(name) do |text|
puts "#{text}"
text.gsub!(regexp) do
#hack to restore magical $~ (and so $1, $2, etc.) in block
eval('lambda{|x| $~ = x}', block).call($~)
block.call #or instance_eval(&block)
instance_eval(&block) works definitely better here.
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