method_missing question

[Peter Szinek]

Hello,

I am using method_missing to build a structure (similar to a tree) like
this:

P.book do
P.title
P.price
end

class P
def self.method_missing(method_name, *args, &block)
#add a node with name 'method_name.to_s' to the tree etc.
end
end

Now, the problem is I would like to write the above example like this:

book do
title
price
end

i.e. without the Ps.
P's sole purpose is to define method_missing - I did not want to
override Object.method_missing since I would like to release this code
to the wild and I think it could collide with my potential future user's
Object.method_missing.

I have then experimented with modules (mimicking namespace
functionality) but that still did not provide the possibility to omit
the class name. I would need something equivalent to include - you can
omit the module name if you include the module - but with classes.

I have no idea if this is possible in Ruby, but is there something like
run this code in a different context or something?

TIA,
Peter

__
http://www.rubyrailways.com

 

[Michael Fellinger]

Hello,

I am using method_missing to build a structure (similar to a tree) like
this:

P.book do
P.title
P.price
end

class P
def self.method_missing(method_name, *args, &block)
#add a node with name 'method_name.to_s' to the tree etc.
end
end

Now, the problem is I would like to write the above example like this:

book do
title
price
end

i.e. without the Ps.
P's sole purpose is to define method_missing - I did not want to
override Object.method_missing since I would like to release this code
to the wild and I think it could collide with my potential future user's
Object.method_missing.

I have then experimented with modules (mimicking namespace
functionality) but that still did not provide the possibility to omit
the class name. I would need something equivalent to include - you can
omit the module name if you include the module - but with classes.

I have no idea if this is possible in Ruby, but is there something like
run this code in a different context or something?

actually, there is - it is called script and you can find it described here:
http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/100429

 

[George Ogata]

Now, the problem is I would like to write the above example like this:

book do
title
price
end

i.e. without the Ps.
P's sole purpose is to define method_missing - I did not want to
override Object.method_missing since I would like to release this code
to the wild and I think it could collide with my potential future user's
Object.method_missing.

I have then experimented with modules (mimicking namespace
functionality) but that still did not provide the possibility to omit
the class name. I would need something equivalent to include - you can
omit the module name if you include the module - but with classes.

I have no idea if this is possible in Ruby, but is there something like
run this code in a different context or something?

Hi Peter,

This sort of thing probably already exists somewhere, but I don't know
what it's called. (The 'script' that Michael mentioned looks like
something else to me... ?)

So anyway, here's a starting point. The trick is to use instance_eval
to change the value of 'self' within the block.

class Node
# Rename all existing methods to start with '__', so they're not
# likely to collide with your attribute names. We'll leave some
# methods alone, since they're necessary for some basic operations.
methods = (instance_methods + private_instance_methods)
methods = methods - %w'__send__ __id__ initialize inspect'
methods.each{|m| alias_method("__#{m}", m); undef_method(m)}

def method_missing(*args, &block)
key, val = *args
if block
args.length == 1 or
raise ArgumentError, "value and block given"
node = Node.new
__instance_variable_set("@#{key}", node)
node.__instance_eval(&block)
return node
else
args.length <= 2 or
raise ArgumentError, "too many arguments"
if args.length > 1
__instance_variable_set("@#{key}", val)
end
return __instance_variable_get("@#{key}")
end
end
end


### Usage

node = Node.new
node.root do
a 1
b 2
c do
d 3
e 4
end
end
p node.root.c.d #=> 3
p node.root.c #=> #<Node:0xb7dd55c4 @d=3, @e=4>
p node #=> #<Node:0xb7ddb8ac @root=#<Node:...>>

 

[Joel VanderWerf]

...
This sort of thing probably already exists somewhere, but I don't know
what it's called. (The 'script' that Michael mentioned looks like
something else to me... ?)

Yes, "script" is something else. It's for loading an external "script"
inside of a module, to confine it to a namespace. It's like "load(...,
true)", but you can access the anonymous module.

It has nothing to do with defining a special syntax like the OP wanted.