Don't rename variables that are only referenced once

[jlukas]

If I have the following implementation:

class MyClass
  def self.instance
    @@instance ||= new
  end
end

Mutant changes it to:

class MyClass
  def self.instance
    @@instance__mutant__ ||= new
  end
end

Which works in exactly the same way. I think mutant should not modify the name of the variable if it is not referenced anywhere else (maybe also looking for var ||= value).

[mbj]

I always wanted not to mutate ivars on the lhs of an or op assgn like this. But the "Variables only refernced once" is also a nice idea to overcome this. I'll look into this idea. Thx.

[mbj]

BTW: I typically dislike and avoid all ||= usages on ivars since this leads to thread safety problems. This is the reason this issue was not pressuring enough for me to get a rid of.