Open classes, constructors and blocks

Ruby
1

Hi all,

I’d like to re-open a class and to re-initialize its original
constructor:

class Foo
def initialize
yield self if block_given?
end
end

class Foo
attr_reader :var
alias foo_initialize initialize
def initialize
foo_initialize
@var = “Foo’s instance var”
end
end

Foo.new { |foo| puts foo.var }

The problem is that the block passed to the new constructor is never
called! Why?
Which is the best way to redefine a constructor when a class is
re-opened?

Thanks!
Andrea

2

Alle 09:49, mercoledì 29 novembre 2006, Andrea F. ha scritto:

called! Why?
When you call foo_initialize from initialize, you’re calling a
completely
unrelated method, so the block won’t be automatically passed to it (this
is
different from when you use super; in that class the block is passed
automatically). In your case, you must pass the block in two ways: the
first
is to create a new block which simply calls yield:

def initialize
@var=“Foo’s instance var”
foo_initialize{yield self}
end

(by the way, you need to assign @var before calling foo_initialize if
you want
its value to be displayed, otherwise you’ll get nil).
The other way is to pass the block as a variable to initialize, using
the &
syntax:

def initialize &block
@var=“Foo’s instance var”
foo_initialize &block
end

I hope this helps

Stefano