Class reloading breaks type-checking

class-reloading.rb

class Foo
end

Foo.object_id                   # => 34581480

f = Foo.new                     # => #<Foo:0x000000041f53c0>

f.class.object_id               # => 34581480

# This just prevents the "const redefined" warning
Object.send(:remove_const, :Foo)

# "Reload" class Foo
class Foo
end

Foo.object_id                   # => 34580180
f.class.object_id               # => 34581480

f.is_a?(Foo)                    # => false
f.class == Foo                  # => false
f.class.name == "Foo"           # => true

@shevegen, Avdi is saying that actual newbs are actually surprised when they first encounter this behavior. Telling someone that they shouldn't be surprised by something that has surprised them is, in effect, a "well, actually".

The fundamental source of the surprise, as you point out, is remove_const. (Or, as I like to think of it, Ruby providing a concrete example of [the first half of] the adage "constants aren't, variables don't.") In many other languages, there's no equivalent -- once a reference is in the symbol table, it's there to stay.

The conversation this was part of was discussing Rails autoloading in development mode. It's not clear to newbs (until it's explained in an example like this) that the autoloading mechanism works this way.