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comp.lang.ruby

Difference between Foo = Class.new and class Foo

Brandon Dimcheff

10/7/2008 2:51:00 PM

I'm playing around with classes and discovered that

class Foo
...
end

and

Foo = Class.new do
...
end

seem to behave slightly differently. I assumed that "class Foo" was
just a shortcut that got translated into "Foo = Class.new", but when I
muck with class in the following way:

class Class
class << self
def new
puts "new called"
super
end
end
end

and then do "Foo = Class.new", I get "new called" printed to stdout.
If I do "class Foo..." I get nothing. So it seems that the "class"
keyword does not end up calling new on Class when you define a new
class. Does anybody know what's going on here? Is something else
called instead?

Thanks,
Brandon
2 Answers

Robert Klemme

10/7/2008 2:57:00 PM

0

2008/10/7 Brandon Dimcheff <bdimchef@wieldim.com>:
> and then do "Foo = Class.new", I get "new called" printed to stdout. If I
> do "class Foo..." I get nothing. So it seems that the "class" keyword does
> not end up calling new on Class when you define a new class. Does anybody
> know what's going on here? Is something else called instead?

Looks like there is a shortcut:

16:55:57 bas$ ruby -e 'set_trace_func lambda {|*a|p a}; class Foo;end'
["line", "-e", 1, nil, #<Binding:0x1002f0d4>, false]
["c-call", "-e", 1, :inherited, #<Binding:0x1002ef80>, Class]
["c-return", "-e", 1, :inherited, #<Binding:0x1002ef44>, Class]
["class", "-e", 1, nil, #<Binding:0x1002ed64>, false]
["end", "-e", 1, nil, nil, false]
16:56:13 bas$ ruby -e 'set_trace_func lambda {|*a|p a}; Foo=Class.new'
["line", "-e", 1, nil, #<Binding:0x1002f0e8>, false]
["c-call", "-e", 1, :new, #<Binding:0x1002f0ac>, Class]
["c-call", "-e", 1, :initialize, #<Binding:0x1002eeb8>, Class]
["c-call", "-e", 1, :inherited, #<Binding:0x1002edb4>, Class]
["c-return", "-e", 1, :inherited, #<Binding:0x1002ed78>, Class]
["c-return", "-e", 1, :initialize, #<Binding:0x1002ec88>, Class]
["c-return", "-e", 1, :new, #<Binding:0x1002eb98>, Class]
16:56:44 bas$

If you need hooks for class creation look closely at ":inherited" above.

Kind regards

robert

--
remember.guy do |as, often| as.you_can - without end

Brandon Dimcheff

10/7/2008 3:17:00 PM

0

hmm, interesting. I'm definitely going to have to use set_trace_func
more often. Do you know if there's any way to tell which c function
is being called for the c-calls? Like how does the ruby method
"inherited" map to rb_... in MRI?

Thanks,
Brandon

On Oct 7, 2008, at 10:56, Robert Klemme wrote:

> 2008/10/7 Brandon Dimcheff <bdimchef@wieldim.com>:
>> and then do "Foo = Class.new", I get "new called" printed to
>> stdout. If I
>> do "class Foo..." I get nothing. So it seems that the "class"
>> keyword does
>> not end up calling new on Class when you define a new class. Does
>> anybody
>> know what's going on here? Is something else called instead?
>
> Looks like there is a shortcut:
>
> 16:55:57 bas$ ruby -e 'set_trace_func lambda {|*a|p a}; class Foo;end'
> ["line", "-e", 1, nil, #<Binding:0x1002f0d4>, false]
> ["c-call", "-e", 1, :inherited, #<Binding:0x1002ef80>, Class]
> ["c-return", "-e", 1, :inherited, #<Binding:0x1002ef44>, Class]
> ["class", "-e", 1, nil, #<Binding:0x1002ed64>, false]
> ["end", "-e", 1, nil, nil, false]
> 16:56:13 bas$ ruby -e 'set_trace_func lambda {|*a|p a}; Foo=Class.new'
> ["line", "-e", 1, nil, #<Binding:0x1002f0e8>, false]
> ["c-call", "-e", 1, :new, #<Binding:0x1002f0ac>, Class]
> ["c-call", "-e", 1, :initialize, #<Binding:0x1002eeb8>, Class]
> ["c-call", "-e", 1, :inherited, #<Binding:0x1002edb4>, Class]
> ["c-return", "-e", 1, :inherited, #<Binding:0x1002ed78>, Class]
> ["c-return", "-e", 1, :initialize, #<Binding:0x1002ec88>, Class]
> ["c-return", "-e", 1, :new, #<Binding:0x1002eb98>, Class]
> 16:56:44 bas$
>
> If you need hooks for class creation look closely at ":inherited"
> above.
>
> Kind regards
>
> robert
>
> --
> remember.guy do |as, often| as.you_can - without end
>