How to redefine a Ruby constant without warning?

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)  endend

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")  endenda = A.newa.show_constantsa.reloada.show_constants

Gives the following output

Foo is ABCBar is DEFFoo is GHIBar 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

Another approach, using $VERBOSE, to suppress warnings, is discussed here: http://mentalized.net/journal/2010/04/02/suppress_warnings_from_ruby/

Update 2020/5/6: In response to the comment that the link is now dead, I am pasting an example here from my old project, though I can't say whether and in what circumstances it is a good approach:

original_verbose = $VERBOSE$VERBOSE = nil # suppress warnings# do stuff that raises warnings you don't care about$VERBOSE = original_verbose

If you want to redefine a value then don't use constants, use a global variable instead ($tau = 2 * Pi), but that's not a good practice too. You should make it an instance variable of a suitable class.

For the other case, Tau = 2 * Pi unless defined?(Tau) is perfectly alright and the most readable, therefore the most elegant solution.