From: Nasir Khan <rubylearner@...>
Date: 2007-05-14T13:14:54+09:00
Subject: argument hash to string to proc to instance variables

It is idiomatic to pass a number of related arguments (usually config
related) as the last (braceless argument) to a method ( heavily used
in Rails ) e.g .

  def my_method(arg1, arg2)
  end

 where arg1 is anything and arg2 is a hash

  my_method("hello", :a=>"nasir", :b => 30, :c="khan")   etc.

It is also quite popular to instance_eval a block to initialize a
number of attributes rather than pass them all upfront to "new".  e.g.

class A
  attr_accessor :a, :b, :c
  def initialize(&block)
     instance_eval(&block) if block_given?
  end
end

x = A.new do
  self.a = "hello";
  self.b = 1;
  self.c = "bye";
end

It is also trivial to use these two techniques together i.e. take the
hash argument in the method and use it to create a proc which can be
evaled as a block  e.g.

  def my_method(arg1, arg2)
     str = "lambda { "
     arg2.each_pair {|k,v| str << sprintf("self.%s=%s;", k, v) }
     str << " }"
     p = eval str
     x = A.new &p
   end
  end

Here "my_method" returns the instance of class A initialized with the
attributes given
as hash which is converted to block and instance_evaled in the
initialize method of class A.

All this works but I am doing *two* evals (one for string to proc in
my_method and one the instance_evaling of block in initialize, not to
mention constructing the string for proc.

Is there is a simpler/faster alternative that I have overlooked?

- Nasir