How to redefine a Ruby constant without warning?

Question

I'm running some Ruby code which evals a Ruby file every time its date changes. In the file, I have constant definitions, like

Tau = 2 * Pi 

and, of course, they make the interpreter display the unwanted "already initialized constant" warning every time, so, I'd like to have the following functions:

def_if_not_defined(:Tau, 2 * Pi) redef_without_warning(:Tau, 2 * Pi) 

I could avoid the warning by writing all my constant definitions like this:

Tau = 2 * Pi unless defined?(Tau) 

but it is inelegant and a bit wet (not DRY).

Is there a better way to def_if_not_defined? And how to redef_without_warning?

--

Solution thanks to Steve:

class Object   def def_if_not_defined(const, value)     mod = self.is_a?(Module) ? self : self.class     mod.const_set(const, value) unless mod.const_defined?(const)   end    def redef_without_warning(const, value)     mod = self.is_a?(Module) ? self : self.class     mod.send(:remove_const, const) if mod.const_defined?(const)     mod.const_set(const, value)   end end  A = 1 redef_without_warning :A, 2 fail 'unit test' unless A == 2 module M   B = 10   redef_without_warning :B, 20 end fail 'unit test' unless M::B == 20 

--

This question is old. The above code is only necessary for Ruby 1.8. In Ruby 1.9, P3t3rU5's answer produces no warning and is simply better.

Answer 1

The following module may do what you want. If not it may provide some pointers to your solution

module RemovableConstants    def def_if_not_defined(const, value)     self.class.const_set(const, value) unless self.class.const_defined?(const)   end    def redef_without_warning(const, value)     self.class.send(:remove_const, const) if self.class.const_defined?(const)     self.class.const_set(const, value)   end end 

And as an example of using it

class A   include RemovableConstants    def initialize     def_if_not_defined("Foo", "ABC")     def_if_not_defined("Bar", "DEF")   end    def show_constants     puts "Foo is #{Foo}"     puts "Bar is #{Bar}"   end    def reload     redef_without_warning("Foo", "GHI")     redef_without_warning("Bar", "JKL")   end  end  a = A.new a.show_constants a.reload a.show_constants 

Gives the following output

Foo is ABC Bar is DEF Foo is GHI Bar is JKL 

Forgive me if i've broken any ruby taboos here as I am still getting my head around some of the Module:Class:Eigenclass structure within Ruby