When is `eval` in Ruby justified?

Question

\"Is \'eval\' supposed to be nasty?\" inspired this one:

Mostly everybody agrees that eval is bad, and in most cases there is more elegant/safer replace

Answer 1

There is one very important use-case for eval() which cannot (AFAIK) be achieved using anything else, and that is to find the corresponding object reference for a binding.

Say you have been passed a block but (for some reason) you need access to object context of the binding, you would do the following:

obj = eval('self', block.binding)

It is also useful to define the following:

class Proc
    def __context__
        eval('self', self.binding)
    end
end