Difference between instance_eval and singleton method

Question

Singleton method is a method that is defined only on one instance.

foo = Foo.new
def foo.case
  #singleton method
end

Doesn't instance_eval do the same thing? Defining a method for a particular instance? What is the difference?

Answer 1

Object#instance_eval is a method, using which you indeed can define method for an object.

Singleton class is a "place", where the singleton method defined for the object "lives".

So these are two absolutely different things.