Created
June 12, 2012 19:08
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Class reloading breaks type-checking
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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.
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It should not be surprising to newbs because the code specifically instructed ruby to remove the constant Foo.
Any other behaviour would be just as surprising, because you would then see that the constant would still exist, despite the code specifically telling ruby to remove that constant before.
If you would want that behaviour different, by treating class Foo the same, then you would have to disallow remove_const, because remove_const could no longer change ANY namespace (classes and modules are constants just as any other upcased first character)