Forward references?

[Peter Seebach]

I am trying to figure out what the cleanest way is to express a class that has
subclasses.

Imagine, if you will:
class Foo
def initialize
@bar = Foo::Bar.new(self)
end
end

class Foo::Bar
def initialize(foo)
@foo = foo
end
end

Is that a good rubyish way to do this? If I put Foo::Bar in
its own file, should foo.rb be responsible for requiring it?
What originally got me thinking was that my habit is to put requires,
includes, and such at the top of the file... But then the
declaration "class Foo::Bar" refers to an undefined constant.

Of course, I can write:
class Foo
end
require 'foo/bar.rb'

Is there a clear preference here in Ruby Style?

-s

 

[Robert Klemme]

I am trying to figure out what the cleanest way is to express a class that has
subclasses.

First of all, your example is about nested classes and not subclasses.

Imagine, if you will:
class Foo
def initialize
@bar = Foo::Bar.new(self)
end
end

class Foo::Bar
def initialize(foo)
@foo = foo
end
end

Is that a good rubyish way to do this? If I put Foo::Bar in
its own file, should foo.rb be responsible for requiring it?
What originally got me thinking was that my habit is to put requires,
includes, and such at the top of the file... But then the
declaration "class Foo::Bar" refers to an undefined constant.

That's not an issue as long as you evaluate that only after the constant
has been defined:

irb(main):001:0> def test() Foo.new end
=> nil
irb(main):002:0> class Foo; end
=> nil
irb(main):003:0> test

Of course, I can write:
class Foo
end
require 'foo/bar.rb'

Is there a clear preference here in Ruby Style?

I would not put these in different files as Foo depends on Foo::Bar and
Foo::Bar depends on Foo.

I'd do

class Foo
def initialize
@bar = Bar.new self
end

class Bar
def initialize(foo)
@foo = foo
end
end
end

irb(main):012:0> Foo.new
=> #<Foo:0x7ff7883c @bar=#<Foo::Bar:0x7ff78738 @foo=#<Foo:0x7ff7883c ...>>>

Another question is whether you really want nested classes or maybe
rather classes in the same namespace. Basically I create nested classes
if the nested class only makes sense in the context of the outer class.
The situation is however different than in Java where all this is much
more strict (and thus clear).

Kind regards

robert

 

[Jeremy Henty]

class Foo
def initialize
@bar = Foo::Bar.new(self)
end
end

[snip]

... If I put Foo::Bar in its own file, should foo.rb be responsible
for requiring it?

I would say yes. My rule of thumb is that any file that explicitly
calls some API must explicitly require/use/#include/... that API.
IOW, batteries *should* be included; don't force your users to make
extra trips to the shops.

Regards,

Jeremy Henty